Why is prayer necessary for christians?

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.

Of Prayer 

 45. Lord's Day 

 Q. 116. Why is prayer necessary for christians? 

A. Because it is the chief part of thankfulness which God requires of us: (a) and also, because God will give his grace and Holy Spirit to those only, who with sincere desires continually ask them of him, and are thankful for them. (b) 

 (a) Ps.50:14 Offer unto God thanksgiving; and pay thy vows unto the most High: Ps.50:15 And call upon me in the day of trouble: I will deliver thee, and thou shalt glorify me. 

(b) Matt.7:7 Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you: Matt.7:8 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened. Luke 11:9 And I say unto you, Ask, and it shall be given you; seek, and ye shall find; knock, and it shall be opened unto you. Luke 11:10 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened. Luke 11:13 If ye then, being evil, know how to give good gifts unto your children: how much more shall your heavenly Father give the Holy Spirit to them that ask him? 1 Thess.5:17 Pray without ceasing. 

 Q. 117. What are the requisites of that prayer, which is acceptable to God, and which he will hear? 

A. First, that we from the heart pray (a) to the one true God only, who has manifested himself in his word, (b) for all things, he has commanded us to ask of him; (c) secondly, that we rightly and thoroughly know our need and misery, (d) that so we may deeply humble ourselves in the presence of his divine majesty; (e) thirdly, that we be fully persuaded that he, notwithstanding that we are unworthy of it, will, for the sake of Christ our Lord, certainly hear our prayer, (f) as he has promised us in his word. (g) 

 (a) John 4:24 God is a Spirit: and they that worship him must worship him in spirit and in truth. Ps.145:18 The LORD is nigh unto all them that call upon him, to all that call upon him in truth. 

(b) Rev.19:10 And I fell at his feet to worship him. And he said unto me, See thou do it not: I am thy fellowservant, and of thy brethren that have the testimony of Jesus: worship God: for the testimony of Jesus is the spirit of prophecy. 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. (c) Rom.8:26 Likewise the Spirit also helpeth our infirmities: for we know not what we should pray for as we ought: but the Spirit itself maketh intercession for us with groanings which cannot be uttered. 1 John 5:14 And this is the confidence that we have in him, that, if we ask any thing according to his will, he heareth us: James 1:5 If any of you lack wisdom, let him ask of God, that giveth to all men liberally, and upbraideth not; and it shall be given him. 

(d) 2 Chron.20:12 O our God, wilt thou not judge them? for we have no might against this great company that cometh against us; neither know we what to do: but our eyes are upon thee. 

(e) Ps.2:11 Serve the LORD with fear, and rejoice with trembling. Ps.34:19 Many are the afflictions of the righteous: but the LORD delivereth him out of them all. Isa.66:2 For all those things hath mine hand made, and all those things have been, saith the LORD: but to this man will I look, even to him that is poor and of a contrite spirit, and trembleth at my word. 

(f) Rom.10:14 How then shall they call on him in whom they have not believed? and how shall they believe in him of whom they have not heard? and how shall they hear without a preacher? James 1:6 But let him ask in faith, nothing wavering. For he that wavereth is like a wave of the sea driven with the wind and tossed. 

(g) John 14:13 And whatsoever ye shall ask in my name, that will I do, that the Father may be glorified in the Son. John 14:14 If ye shall ask any thing in my name, I will do it. John 16:23 And in that day ye shall ask me nothing. Verily, verily, I say unto you, Whatsoever ye shall ask the Father in my name, he will give it you. Dan.9:17 Now therefore, O our God, hear the prayer of thy servant, and his supplications, and cause thy face to shine upon thy sanctuary that is desolate, for the Lord's sake. Dan.9:18 O my God, incline thine ear, and hear; open thine eyes, and behold our desolations, and the city which is called by thy name: for we do not present our supplications before thee for our righteousnesses, but for thy great mercies. 

(h) Matt.7:8 For every one that asketh receiveth; and he that seeketh findeth; and to him that knocketh it shall be opened. Ps.27:8 When thou saidst, Seek ye my face; my heart said unto thee, Thy face, LORD, will I seek. 

 Q. 118. What has God commanded us to ask of him? 

A. All things necessary for soul and body; (a) which Christ our Lord has comprised in that prayer he himself has taught us. 

(a) James 1:17 Every good gift and every perfect gift is from above, and cometh down from the Father of lights, with whom is no variableness, neither shadow of turning. Matt.6:33 But seek ye first the kingdom of God, and his righteousness; and all these things shall be added unto you. 

 Q. 119. What are the words of that prayer? 

(a) A. Our Father which art in heaven, 

1 Hallowed be thy name. 

2 Thy kingdom come. 

3 Thy will be done on earth, as it is in heaven. 

4 Give us this day our daily bread. 

5 And forgive us our debts, as we forgive our debtors. 

6 And lead us not into temptation, but deliver us from evil. For thine is the kingdom, and the power, and the glory, for ever. Amen. 

 (a) Matt.6:9 After this manner therefore pray ye: 

Our Father which art in heaven, 

Hallowed be thy name. 

Matt.6:10 Thy kingdom come. Thy will be done in earth, as it is in heaven. 

Matt.6:11 Give us this day our daily bread. 

Matt.6:12 And forgive us our debts, as we forgive our debtors. 

Matt.6:13 And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen. 

Luke 11:2 And he said unto them, When ye pray, say, 

Our Father which art in heaven, 

Hallowed be thy name. 

Thy kingdom come. 

Thy will be done, as in heaven, so in earth. 

Luke 11:3 Give us day by day our daily bread. 

Luke 11:4 And forgive us our sins; for we also forgive every one that is indebted to us. And lead us not into temptation; but deliver us from evil.

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