Prayer is a response to promises, that is, to the assurances of God’s future grace.
Prayer is drawing on the account where God has deposited all his promises of future grace.
Prayer is not hoping in the dark that there might be a God of good intentions out there. Prayer goes to the bank every day and draws on promises for the future grace needed for that day.
Prayer is the confident plea for God to make good on his promises of future grace for Christ’s sake