The way the woman caught in adultery was being treated by the Jewish leaders was not a good example of warning the sinner (John 8:1-6). Their intent to stone her was not a warning to her but to others who might be thinking of adultery. Jesus' instruction to her was to leave her life of sin. She had already been publicly humiliated. There was no need for him to say more.
A word of warning would ordinarily be given in private, but the woman had been brought into the main public area of the temple. It would ordinarily be done one-on-one, but a group of men accosted her. It would ordinarily be done with compassion and mercy, but the leaders wanted to shame her and make an example of her. They were using her for their own ends. There was nothing gentle about it.
For Reflection: How would I react if someone were to warn me about a sin? How would I want to be approached? Before we begin to warn someone else, a time of intercessory prayer for that person would be helpful, and perhaps all that is necessary.
Let us pray. Jesus, if I am persisting in sin and hardened to it, I hope that you will send someone to warn me and that I will be open to that warning.