1 Corinthians 10:12

Wherefore let him that thinketh he standeth take heed lest he fall.

Therefore let him who thinks he stands be careful that he doesn't fall.

Wherefore let him that thinketh he standeth take heed lest he fall.

so that he who is thinking to stand -- let him observe, lest he fall.

So the one who thinks he is standing firm should be careful not to fall.