John Gill Commentary Luke 21:15

"for I will give you a mouth and wisdom, which all your adversaries shall not be able to withstand or to gainsay." — Luke 21:15 (ASV)

For I will give you a mouth A faculty of speaking, a freedom of expression, a door of utterance, a good degree of elocution, to speak properly, pertinently and freely to any point: and wisdom; to answer with great propriety, and in the most prudent manner, to any difficult and ensnaring question; and to furnish with such knowledge of the Gospel, and with such gifts and abilities to preach and defend it, that they should be able to give a clear and distinct account of it, and prove every point in it, by the most strong and convincing arguments, and vindicate it against all objections:

which all your adversaries shall not be able to gainsay or resist.

This was remarkably fulfilled in Peter, and John, and in Stephen, (Acts 4:13Acts 4:14) (6:10) . The first word, "gainsay", is left out in the Syriac and Persic versions.