Pray in faith

From Calvin's commentary:

Matthew 7:7. Ask, and it shall be given you It is an exhortation to prayer: and as in this exercise of religion, which ought to be our first concern, we are so careless and sluggish, Christ presses the same thing upon us under three forms of expression. There is no superfluity of language, when he says, Ask, seek, knock: but lest the simple doctrine should be unimpressive, he perseveres in order to rouse us from our inactivity. Such is also the design of the promises that are added, Ye shall find, it shall be given to you, and it shall be opened Nothing is better adapted to excite us to prayer than a full conviction that we shall be heard. Those who doubt can only pray in an indifferent manner; and prayer, unaccompanied by faith, is an idle and unmeaning ceremony. Accordingly, Christ, in order to excite us powerfully to this part of our duty, not only enjoins what we ought to do, but promises that our prayers shall not be fruitless.