Dear friends, I had been eagerly planning to write to you about the
salvation we all share. But now I find that I must write about
something else, urging you to defend the faith that God has entrusted
once for all time to his holy people. I say this because some
ungodly people have wormed their way into your churches, saying that
God’s marvelous grace allows us to live immoral lives. The
condemnation of such people was recorded long ago, for they have
denied our only Master and Lord, Jesus Christ.

...

And you must show mercy to those whose faith is wavering. Rescue
others by snatching them from the flames of judgment. Show mercy to
still others, but do so with great caution, hating the sins that
contaminate their lives.

Jude 1:3-4,22-23 (NLT)