Proofs:

What thing soever I command you, observe to do it: thou shalt not add thereto, nor diminish from it. (Deut. 12:32).

And Samuel said, Hath the LORD as great delight in burnt offerings and sacrifices, as in obeying the voice of the LORD? Behold, to obey is better than sacrifice, and to hearken than the fat of rams. (1 Sam. 15:22).

Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. (1 John 3:4).

For as by one man's disobedience many were made sinners, so by the obedience of one shall many be made righteous. (Rom. 5:19).

109. Since God had said, "Thou shalt not kill", was it not wicked for Israel to kill the Canaanites?
Answer: No; because God commanded Israel to kill the Canaanites. There is a time to kill and a time to keep alive. God knows the one time and the other, and when He commands, man has nothing to do but obey. God can do as He pleases. None can call Him in question.

Proofs:

And when the LORD thy God shall deliver them before thee; thou shalt smite them, and utterly destroy them; thou shalt make no covenant with them, nor shew mercy unto them: (Deut. 7:2).

Circumcise therefore the foreskin of your heart, and be no more stiffnecked. (Deut. 10:16).

To every thing there is a season, and a time to every purpose under the heaven: A time to be born, and a time to die; a time to plant, and a time to pluck up that which is planted; A time to kill, and a time to heal; a time to break down, and a time to build up; (Ecc. 3:1-3).

(When the Lord commands -- see 1 Sam. 15:3, 9, 23, 33)

Cursed be he that doeth the work of the LORD deceitfully, and cursed be he that keepeth back his sword from blood. (Jer. 48:10).

And all the inhabitants of the earth are reputed as nothing: and he doeth according to his will in the army of heaven, and among the inhabitants of the earth: and none can stay his hand, or say unto him, What doest thou? (Dan. 4:35).

Whatsoever the LORD pleased, that did he in heaven, and in earth, in the seas, and all deep places. (Psa. 135:6).