John Gill Commentary Mark 11:24

"Therefore I say unto you, All things whatsoever ye pray and ask for, believe that ye receive them, and ye shall have them." — Mark 11:24 (ASV)

Therefore I say unto you
For encouragement in prayer more particularly, without which nothing should be attempted, and especially which is above the power of nature, and is of a miraculous kind:

whatsoever things you desire when you pray ;
that is, according to the revealed will of God, is for the confirmation of his Gospel, and for the glory of his name:

believe that you receive [them], and you shall have [them] ;
the petitions that are desired, and the things asked in them: that is, be as much assured of having them, as if you had already received them, and you shall have them; for the sense can never be, that they should believe they received them before they had them; this would be a contradiction in terms; and Beza's ancient copy, and one of Stephens's copies read it, "believe that you shall receive", as in (Matthew 21:22) , and so the Vulgate Latin version; with which agree the Arabic and Ethiopic versions, which render it, "believe that you shall enjoy", or "obtain"; and the Syriac version, "believe that you are about to receive"; and great faith it is so to believe; and this is the prayer of faith; see (1 John 5:14 1 John 5:15) .