'Be on Your Guard' in the Bible

So be on your guard that the very source of light in you is not darkness.

In the meantime, after so many thousands of the people had gathered that they were stepping on one another, Jesus began speaking first of all to His disciples, “Be continually on your guard against the leaven of the Pharisees [that is, their pervasive, corrupting influence and teaching], which is hypocrisy [producing self-righteousness].

And to the people He said, "Take care, be on your guard against all covetousness, for no one's life consists in the superabundance of his possessions."

Pay attention and always be on guard [looking out for one another]! If your brother sins and disregards God’s precepts, solemnly warn him; and if he repents and changes, forgive him.

"Be on your guard against the Teachers of the Law, who delight to walk about in long robes, and like to be greeted in the streets with respect, and to have the best seats in the Synagogues, and places of honor at dinner.

He said, “Be careful and see to it that you are not misled; for many will come in My name [appropriating for themselves the name Messiah which belongs to Me alone], saying, ‘I am He,’ and, ‘The time is near!’ Do not follow them.

“But be on guard, so that your hearts are not weighed down and depressed with the giddiness of debauchery and the nausea of self-indulgence and the worldly worries of life, and then that day [when the Messiah returns] will not come on you suddenly like a trap;

"So be on your guard at all times, praying that you may be worthy to escape these things that shall come to pass, and to take your stand in the presence of the Son of man."