“For this reason I tell you, whatever you pray and ask for, believe that you have received it, and it will be yours.”
Often, when the Lord made a promise to Israel, he put it in the past tense (see Deuteronomy 3.2, for example), to indicate how sure was his word. Jesus does the same about prayer requests.
The Lord is able to bless, and he desires to bless. He bristled when the possessed boy’s father said, “If you can” Mark 9.22-23. The issue is not his ability or desire, but our willingness to believe.