What does God forbid in the eighth commandment?

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.

42. Lord's Day 

Q. 110. What does God forbid in the eighth commandment? 

A. God forbids not only those thefts, (a) and robberies, (b) which are punishable by the magistrate; but he comprehends under the name of theft all wicked tricks and devices, whereby we design to appropriate to ourselves the goods which belong to our neighbour: (c) whether it be by force, or under the appearance of right, as by unjust weights, ells, measures, fraudulent merchandise, (d) false coins, usury, (e) or by any other way forbidden by God; as also all covetousness, (f) all abuse and waste of his gifts. (g) 

(a) 1 Cor.6:10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God. 

(b) 1 Cor.5:10 Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world. Isa.33:1 Woe to thee that spoilest, and thou wast not spoiled; and dealest treacherously, and they dealt not treacherously with thee! when thou shalt cease to spoil, thou shalt be spoiled; and when thou shalt make an end to deal treacherously, they shall deal treacherously with thee. 

(c) Luke 3:14 And the soldiers likewise demanded of him, saying, And what shall we do? And he said unto them, Do violence to no man, neither accuse any falsely; and be content with your wages. 1 Thess.4:6 That no man go beyond and defraud his brother in any matter: because that the Lord is the avenger of all such, as we also have forewarned you and testified. 

(d) Prov.11:1 A false balance is abomination to the LORD: but a just weight is his delight. Prov.16:11 A just weight and balance are the LORD'S: all the weights of the bag are his work. Ezek.45:9 Thus saith the Lord GOD; Let it suffice you, O princes of Israel: remove violence and spoil, and execute judgment and justice, take away your exactions from my people, saith the Lord GOD. Ezek.45:10 Ye shall have just balances, and a just ephah, and a just bath. Ezek.45:11 The ephah and the bath shall be of one measure, that the bath may contain the tenth part of an homer, and the ephah the tenth part of an homer: the measure thereof shall be after the homer. Ezek.45:12 And the shekel shall be twenty gerahs: twenty shekels, five and twenty shekels, fifteen shekels, shall be your maneh. Deut.25:13 Thou shalt not have in thy bag divers weights, a great and a small. Deut.25:14 Thou shalt not have in thine house divers measures, a great and a small. Deut.25:15 But thou shalt have a perfect and just weight, a perfect and just measure shalt thou have: that thy days may be lengthened in the land which the LORD thy God giveth thee. Deut.25:16 For all that do such things, and all that do unrighteously, are an abomination unto the LORD thy God. 

(e) Ps.15:5 He that putteth not out his money to usury, nor taketh reward against the innocent. He that doeth these things shall never be moved. Luke 6:35 But love ye your enemies, and do good, and lend, hoping for nothing again; and your reward shall be great, and ye shall be the children of the Highest: for he is kind unto the unthankful and to the evil. 

(f) 1 Cor.6:10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God. 

(g) Prov.23:20 Be not among winebibbers; among riotous eaters of flesh: Prov.23:21 For the drunkard and the glutton shall come to poverty: and drowsiness shall clothe a man with rags. Prov.21:20 There is treasure to be desired and oil in the dwelling of the wise; but a foolish man spendeth it up. 

Q. 111. But what does God require in this commandment? 

A. That I promote the advantage of my neighbour in every instance I can or may; and deal with him as I desire to be dealt with by others: (a) further also that I faithfully labour, so that I may be able to relieve the needy. (b) 

(a) Matt.7:12 Therefore all things whatsoever ye would that men should do to you, do ye even so to them: for this is the law and the prophets. 

(b) Eph.4:28 Let him that stole steal no more: but rather let him labour, working with his hands the thing which is good, that he may have to give to him that needeth.

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