'Firm' in the Bible

Therefore, I will always be ready to remind you of these things, even though you already know them and are established in the truth which is held firmly in your grasp.

Therefore, [let me warn you] beloved, knowing these things beforehand, be on your guard so that you are not carried away by the error of unprincipled men [who distort doctrine] and fall from your own steadfastness [of mind, knowledge, truth, and faith],