The answer of our Lord is adapted to the petition of the child's father. He had said: If thou canst do any thing, have mercy on us: and Christ answered: If thou canst believe Thus when the leper said: If thou wilt, thou canst make me clean, he answered: I will, be thou made clean. (Ven Bede)
All things are possible to him that believeth. The sense is not, as if he that believeth could do all things; but that any thing might be done by the divine power and goodness, in favour of him that had a firm and lively faith. (Witham)
The Scripture indicates that this man was extremely weak in faith, as is evident at four points: from Christ’s saying that “All things are possible to him that believes;” from the saying of the man himself as he approached, “Help me in my unbelief;” from Christ’s commanding the devil to “enter no more into him;” and from the man’s saying again to Christ, “If you can.” The Gospel of St. Matthew, Homily
