"be awake and alert" or "watch out." Christian leaders being alert about anyone that may harm the community of believers is spoken of as if they were guards in an army watching out for the enemy army. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "tears" refers to Paul's crying because of the strong emotion of concern he felt while he was warning the people. (See: [[rc://en/ta/man/translate/figs-metonymy]])