John Trapp on Mark 9:22-23

Verse 22. It hath cast him into the fire, &c.] So doth blind zeal deal by them in whom it is. But if thou canst doe any thing] This wofull father had no further patience to parley; but through weaknesse of faith, and strength of affection to his distressed child breaks off his tale, and begs present help. Hee that beleeveth, maketh no haste, Esay 28. 16.