Albert Barnes on Matthew 26:53

Thinkest thou, etc. Jesus says, that not only would Peter endanger himself, but his resistance implied a distrust of the protection of God, and was an improper resistance of his will. If it had been proper that they should be rescued, God could easily have furnished far more efficient aid than that of Peter--a mighty host of angels.

Twelve legions. A legion was a division of the Roman army amounting to more than six thousand men. Mt 8:29. The number twelve was mentioned, perhaps, in reference to the number of his apostles, and himself. Judas being away, but eleven disciples remained. God could guard him, and each disciple, with a legion of angels; that is, God could easily protect him, if he should pray to him, and if it was his will.

(w) "angels" 2Kgs 6:17, Dan 7:10, Mt 4:11