Ver. 19. If you have faith as a grain of mustard-seed. Christ insinuates to his apostles, as if they had not yet faith enough to work great miracles, which require a firm faith joined with a lively confidence in God. The mustard-seed is brought in with an allusion to its hot and active qualities. (Witham) — That is, a perfect faith; which, in its properties and its fruits, resembles the grain of mustard-seed in the parable. (Chap. xii.[xiii.?] 31.) (Challoner) — By faith is here understood, not that virtue by which we assent to all things that are to be believed of Christ, the first, of the theological virtues, in which the apostles were not deficient, but that confidence in the power and goodness of God, that he will on such an occasion exert these, his attributes, in favour of the supplicant. To have a true faith of this kind, and free from all presumption, is a great and high privilege, which the Holy Ghost breathes into such only as he pleases. (Jansenius) — Examples of this efficacious faith are given by St. Paul. (Hebrews chap. ii.[xi.?]) St. Gregory of Neo-Cæsarea is also related, by Eusebius and Ven. Bede, to have removed by the efficacy of his faith a rock, which obstructed the building of a church; thus literally fulfilling the promise of Jesus Christ. (Tirinus) — The faith of the apostles, especially of those that had not been present at the transfiguration, was not perfect and complete in all its parts, till after the resurrection and ascension of Jesus Christ, and the descent of the Holy Ghost. (Haydock) — St. Jerome understands by mountains, things the most difficult to be effected.