John 8:3-11 And the scribes and Pharisees brought unto him a woman taken in adultery; and when they had set her in the midst, They say unto him, Master, this woman was taken in adultery, in the very act. Now Moses in the law commanded us, that such should be stoned: but what say thou? This they said, tempting him, that they might have to accuse him. But Jesus stooped down, and with his finger wrote on the ground, as though he heard them not. So when they continued asking him, he lifted up himself, and said unto them, He that is without sin among you, let him first cast a stone at her. And again he stooped down, and wrote on the ground. And they which heard it, being convicted by their own conscience, went out one by one, beginning at the eldest, even unto the last: and Jesus was left alone, and the woman standing in the midst. When Jesus had lifted up himself, and saw none but the woman, he said unto her, Woman, where are those thine accusers? hath no man condemned thee? She said, No man, Lord. And Jesus said unto her, Neither do I condemn thee: go, and sin no more. 

The scribes and Pharisees attempted, yet again, to snare Jesus to arrest Him by bringing a woman that was taken in adultery. Had He contradicted Moses (Lev. 20:10; Deut. 22:22-24), He would have been condemned as a false prophet. Had He condemned the woman to death He would have been accused to the Romans as usurping authority, so He merely wrote on the ground as if He did not hear them. When they continued to ask, He told them that the sinless ones should first cast a stone. It is not recorded what He wrote on the ground.

Capital punishment by stoning was lawful (Ex. 19:13; Deut. 13:10; 17:5; 22:21). The Jewish method of execution was to cast the criminal from a 10 or 12 feet scaffold half-naked, with hands tied in the back. The witnesses did the pushing with great force and if this did not kill him a witness then would take a large stone and dash it upon the breast. On occasions where mobs stoned a man no scaffold was used, but certain accusers threw the first stones and then all could throw until the victim was dead (Num. 15:36; Jos. 7:25; 1Kings 21:13; Acts 7:58-59; 14:19; 2Cor. 11:25).

Conscience is a wonderful thing. It is the faculty that decides the lawfulness of our actions as to right and wrong (Rom. 2:12-16). The causes of their conviction was their own evil designs against Him, not so much against her; their failure to include the man who was guilty with the woman; what Christ wrote on the ground; the challenge to start throwing if they were sinless themselves; their hypocrisy which was known to Christ and others present; and their guilt of committing the same sin (Rom. 2:1).

As they were convicted by their own consciences, they, her accusers, started to depart, leaving the woman in the midst of the disciples and others who were present.

Jesus did not say He did not condemn adultery as a sin. He simply forgave the woman, as He had done others who were sinful (Matt. 9:1-8; Luke 7:37-50). He was not a magistrate and since no man of her accusers stayed to condemn, He was not going to pass sentence on the woman, taking it upon Himself to execute the law of Moses. He had to avoid the Jews accusing Him of taking magisterial authority in His own hands. Then, too, Christ came to save men, not to destroy them, so forgiveness of her sin was as much His obligation then as it still is when anyone repents and turns from sin (Matt. 12:31-32; 1Jn. 1:9). He frankly told her to sin no more, proving He did condemn adultery as a sin. He did so elsewhere (Matt. 5:27-32; 19:9, 18-19).