What difference is there between the Lord's supper and the popish mass?

Heidelberg Catechism (extended)

The Catechism
Method of Instruction in the Christian Religion
As the Same is Taught in the Reformed Churches and Schools

(with the Scripture references written out)

Note. This Catechism is fully based on the Scriptures. The references to Scripture are indicated in parentheses with a letter. For example, the letter (a) points to the texts (a) placed after the answer.

30. Lord's Day 

Q. 80. What difference is there between the Lord's supper and the popish mass? 

A. The Lord's supper testifies to us, that we have a full pardon of all sin by the only sacrifice of Jesus Christ, which he himself has once accomplished on the cross; (a) and, that we by the Holy Ghost are ingrafted into Christ, (b) who, according to his human nature is now not on earth, but in heaven, at the right hand of God his Father, (c) and will there be worshipped by us. (d) But the mass teaches, that the living and dead have not the pardon of sins through the sufferings of Christ, unless Christ is also daily offered for them by the priests; and further, that Christ is bodily under the form of bread and wine, and therefore is to be worshipped in them; so that the mass, at bottom, is nothing else than a denial of the one sacrifice and sufferings of Jesus Christ, and an accursed idolatry. (e) 

(a) Heb.7:27 Who needeth not daily, as those high priests, to offer up sacrifice, first for his own sins, and then for the people's: for this he did once, when he offered up himself. Heb.9:12 Neither by the blood of goats and calves, but by his own blood he entered in once into the holy place, having obtained eternal redemption for us. Heb.9:25 Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others; Heb.9:26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. Heb.9:27 And as it is appointed unto men once to die, but after this the judgment: Heb.9:28 So Christ was once offered to bear the sins of many; and unto them that look for him shall he appear the second time without sin unto salvation. Heb.10:10 By the which will we are sanctified through the offering of the body of Jesus Christ once for all. Heb.10:12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; Heb.10:13 From henceforth expecting till his enemies be made his footstool. Heb.10:14 For by one offering he hath perfected for ever them that are sanctified. John 19:30 When Jesus therefore had received the vinegar, he said, It is finished: and he bowed his head, and gave up the ghost. Matt.26:28 For this is my blood of the new testament, which is shed for many for the remission of sins. Luke 22:19 And he took bread, and gave thanks, and brake it, and gave unto them, saying, This is my body which is given for you: this do in remembrance of me. Luke 22:20 Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you. 

(b) 1 Cor.6:17 But he that is joined unto the Lord is one spirit. 1 Cor.10:16 The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? 

(c) Heb.1:3 Who being the brightness of his glory, and the express image of his person, and upholding all things by the word of his power, when he had by himself purged our sins, sat down on the right hand of the Majesty on high; Heb.8:1 Now of the things which we have spoken this is the sum: We have such an high priest, who is set on the right hand of the throne of the Majesty in the heavens; Heb.8:2 A minister of the sanctuary, and of the true tabernacle, which the Lord pitched, and not man. John 20:17 Jesus saith unto her, Touch me not; for I am not yet ascended to my Father: but go to my brethren, and say unto them, I ascend unto my Father, and your Father; and to my God, and your God. 

(d) Matt.6:20 But lay up for yourselves treasures in heaven, where neither moth nor rust doth corrupt, and where thieves do not break through nor steal: Matt.6:21 For where your treasure is, there will your heart be also. John 4:21 Jesus saith unto her, Woman, believe me, the hour cometh, when ye shall neither in this mountain, nor yet at Jerusalem, worship the Father. John 4:22 Ye worship ye know not what: we know what we worship: for salvation is of the Jews. John 4:23 But the hour cometh, and now is, when the true worshippers shall worship the Father in spirit and in truth: for the Father seeketh such to worship him. John 4:24 God is a Spirit: and they that worship him must worship him in spirit and in truth. Luke 24:52 And they worshipped him, and returned to Jerusalem with great joy: Acts 7:55 But he, being full of the Holy Ghost, looked up stedfastly into heaven, and saw the glory of God, and Jesus standing on the right hand of God, Acts 7:56 And said, Behold, I see the heavens opened, and the Son of man standing on the right hand of God. Col.3:1 If ye then be risen with Christ, seek those things which are above, where Christ sitteth on the right hand of God. Philip.3:20 For our conversation is in heaven; from whence also we look for the Saviour, the Lord Jesus Christ: Philip.3:21 Who shall change our vile body, that it may be fashioned like unto his glorious body, according to the working whereby he is able even to subdue all things unto himself. 1 Thess.1:10 And to wait for his Son from heaven, whom he raised from the dead, even Jesus, which delivered us from the wrath to come. Heb.9:6 Now when these things were thus ordained, the priests went always into the first tabernacle, accomplishing the service of God. Heb.9:7 But into the second went the high priest alone once every year, not without blood, which he offered for himself, and for the errors of the people: Heb.9:8 The Holy Ghost this signifying, that the way into the holiest of all was not yet made manifest, while as the first tabernacle was yet standing: Heb.9:9 Which was a figure for the time then present, in which were offered both gifts and sacrifices, that could not make him that did the service perfect, as pertaining to the conscience; Heb.9:10 Which stood only in meats and drinks, and divers washings, and carnal ordinances, imposed on them until the time of reformation. 

(e) Heb.9:26 For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself. Heb.10:12 But this man, after he had offered one sacrifice for sins for ever, sat down on the right hand of God; Heb.10:14 For by one offering he hath perfected for ever them that are sanctified. Heb.10:19 Having therefore, brethren, boldness to enter into the holiest by the blood of Jesus, Heb.10:20 By a new and living way, which he hath consecrated for us, through the veil, that is to say, his flesh; Heb.10:21 And having an high priest over the house of God; Heb.10:22 Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water. Heb.10:23 Let us hold fast the profession of our faith without wavering; (for he is faithful that promised;) Heb.10:24 And let us consider one another to provoke unto love and to good works: Heb.10:25 Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching. Heb.10:26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, Heb.10:27 But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. Heb.10:28 He that despised Moses' law died without mercy under two or three witnesses: Heb.10:29 Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? Heb.10:30 For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. Heb.10:31 It is a fearful thing to fall into the hands of the living God. 

Q. 81. For whom is the Lord's supper instituted? 

A. For those who are truly sorrowful for their sins, and yet trust that these are forgiven them for the sake of Christ; and that their remaining infirmities are covered by his passion and death; and who also earnestly desire to have their faith more and more strengthened, and their lives more holy; but hypocrites, and such as turn not to God with sincere hearts, eat and drink judgment to themselves. (a) 

(a) 1 Cor.10:19 What say I then? that the idol is any thing, or that which is offered in sacrifice to idols is any thing? 1 Cor.10:20 But I say, that the things which the Gentiles sacrifice, they sacrifice to devils, and not to God: and I would not that ye should have fellowship with devils. 1 Cor.10:21 Ye cannot drink the cup of the Lord, and the cup of devils: ye cannot be partakers of the Lord's table, and of the table of devils. 1 Cor.10:22 Do we provoke the Lord to jealousy? are we stronger than he? 1 Cor.11:28 But let a man examine himself, and so let him eat of that bread, and drink of that cup. 1 Cor.11:29 For he that eateth and drinketh unworthily, eateth and drinketh damnation to himself, not discerning the Lord's body. 

Q. 82. Are they also to be admitted to this supper, who, by confession and life, declare themselves unbelieving and ungodly? 

A. No; for by this, the covenant of God would be profaned, and his wrath kindled against the whole congregation; (a) therefore it is the duty of the christian church, according to the appointment of Christ and his apostles, to exclude such persons, by the keys of the kingdom of heaven, till they show amendment of life. 

(a) 1 Cor.11:20 When ye come together therefore into one place, this is not to eat the Lord's supper. 1 Cor.11:34 And if any man hunger, let him eat at home; that ye come not together unto condemnation. And the rest will I set in order when I come. Isa.1:11 To what purpose is the multitude of your sacrifices unto me? saith the LORD: I am full of the burnt offerings of rams, and the fat of fed beasts; and I delight not in the blood of bullocks, or of lambs, or of he goats. Isa.1:12 When ye come to appear before me, who hath required this at your hand, to tread my courts? Isa.1:13 Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting. Isa.1:14 Your new moons and your appointed feasts my soul hateth: they are a trouble unto me; I am weary to bear them. Isa.1:15 And when ye spread forth your hands, I will hide mine eyes from you: yea, when ye make many prayers, I will not hear: your hands are full of blood. Isa.66:3 He that killeth an ox is as if he slew a man; he that sacrificeth a lamb, as if he cut off a dog's neck; he that offereth an oblation, as if he offered swine's blood; he that burneth incense, as if he blessed an idol. Yea, they have chosen their own ways, and their soul delighteth in their abominations. Jer.7:21 Thus saith the LORD of hosts, the God of Israel; Put your burnt offerings unto your sacrifices, and eat flesh. Jer.7:22 For I spake not unto your fathers, nor commanded them in the day that I brought them out of the land of Egypt, concerning burnt offerings or sacrifices: Jer.7:23 But this thing commanded I them, saying, Obey my voice, and I will be your God, and ye shall be my people: and walk ye in all the ways that I have commanded you, that it may be well unto you. Ps.50:16 But unto the wicked God saith, What hast thou to do to declare my statutes, or that thou shouldest take my covenant in thy mouth?

Source: http://www.ccel.org/creeds/heidelberg-cat-ext.txt