Matthew 7:7

Ask and it shall be given you
This is to be understood of asking of God in prayer, for such things as are wanting; whether of a temporal nature, as food and raiment, which Christ, in the former chapter, had warned against an immoderate and anxious concern for; or of a spiritual nature, as grace, and wisdom to behave in a proper manner, both towards God and men: and such, who ask according to the will of God, in the name of Christ, and under the direction, guidance, and influence of the Spirit, who ask in faith and fear, and with submission to the divine will, shall have what they ask for; not as what they deserve, but as a free gift.

Seek, and ye shall find.
This is still meant of prayer, and of seeking God, his face and favour: which such shall find, who seek in a right way, by Christ, and with their whole hearts, diligently:

knock and it shall be opened unto you
as beggars do, who use much importunity for relief and assistance. So men should stand and knock at the door of mercy, which will not always be shut against them. Faith in prayer is a key that opens this door, when a poor soul finds grace and mercy to help it in time of need. Our Lord's design is to express the nature, fervour, and constancy of prayer, and to encourage to it.