The Heidelberg Catechism: Lord's Day 43

112. Question: What is required in the ninth commandment?

 Answer: I must not give false testimony against anyone, twist no one’s words,  not gossip or slander, nor condemn or join in condemning anyone rashly and  unheard.[1] Rather, I must avoid all lying and deceit as the devil’s own works,
under penalty of God’s heavy wrath.[2] In court and everywhere else, I must love
the truth,[3] speak and confess it honestly, and do what I can to defend and promote my neighbor’s honor and reputation.[4]

 [1] Ps. 15; Prov. 19:5, 9; 21:28; Matt. 7:1; Luke 6:37; Rom. 1:28-32. [2] Lev. 19:11, 12; Prov. 12:22; 13:5; John 8:44; Rev. 21:8. [3] I Cor. 13:6; Eph. 4:25. [4] I Pet. 3:8, 9; 4:8.

The Heidelberg Catechism: Lord's Day 42

110. Question: What does God forbid in the eighth commandment?

 Answer: God forbids not only outright theft and robbery[1] but also such wicked schemes and devices as false weights and measures, deceptive merchandising, counterfeit money, and usury;[2] we must not defraud our neighbor in any way, whether by force or by show of right.[3] In addition God forbids all greed[4] and all abuse or squandering of His gifts.[5]

 [1] Ex. 22:1; I Cor. 5:9, 10; 6:9, 10. [2] Deut. 25:13-16; Ps. 15:5; Prov. 11:1; 12:22; Ezek. 45:9-12; Luke 6:35. [3] Mic. 6:9-11; Luke 3:14; James 5:1-6. [4] Luke 12:15; Eph. 5:5. [5] Prov. 21:20; 23:20, 21; Luke 16:10-13.

 111. Question: What does God require of you in this commandment?

 Answer: I must promote my neighbor’s good wherever I can and may, deal with him as I would like others to deal with me, and work faithfully so that I may be able to give to those in need.[1]

 [1] Is. 58:5-10; Matt. 7:12; Gal. 6:9, 10; Eph. 4:28.