“It is harder for the heart to be furnished with assurance than for the mind to be endowed with thought.”
So writes John Calvin in in third book of The Institutes of the Christian Religion. In other words–it’s easier to fill your mind with information than to make your heart strong in faith.
God’s answer for this is Himself–His Spirit sent into our hearts. Calvin observes: “The Spirit accordingly serves as a seal, to seal up in our hearts those very promises, the certainty of which [He] has previously impressed upon our minds; and takes the place of a guarantee to confirm and establish them.” Just thinking of this is enough to make you praise God. God himself comes personally to help us grasp and hold onto the things our hearts most need–assurance of his love, mercy, and final victory. This is what God himself does for us.
But is there anything we can do? Can we take steps to strengthen ourselves, or be strengthened in the things we most need to be strong in? Yes, says Calvin. Give attention to God’s word. And don’t let it stay on the surface of your mind. Do whatever you have to do to send it deep within–“The Word of God is not received by faith if it flits about in the top of the brain, but when it takes root in the depth of the heart that it may be an invincible defense to withstand and drive off all the stratagems of temptation.”