en_tn_lite_do_not_use/2pe/03/17.md

Therefore, beloved, since you know these things

The truth about the patience of God and the teachings of these false teachers.

guard yourselves

"Be aware and protect yourself"

you lose your own faithfulness

You start doubting your faith in Jesus Christ.

But grow in...

Peter describes how the believers are to grow in their faithfulness and guard against the false teachers.