'Firm' in the Bible

Therefore let the one who thinks he stands firm [immune to temptation, being overconfident and self-righteous], take care that he does not fall [into sin and condemnation].

I praise and appreciate you because you remember me in everything and you firmly hold to the traditions [the substance of my instructions], just as I have passed them on to you.

Therefore, my beloved brothers and sisters, be steadfast, immovable, always excelling in the work of the Lord [always doing your best and doing more than is needed], being continually aware that your labor [even to the point of exhaustion] in the Lord is not futile nor wasted [it is never without purpose].

Be on guard; stand firm in your faith [in God, respecting His precepts and keeping your doctrine sound]. Act like [mature] men and be courageous; be strong.