Brainerd lived the life of holiness and prayer. His diary is full and monotonous with the record of his seasons of fasting, meditation, and retirement. The time he spent in private prayer amounted to many hours daily. "When I return home," he said, "and give myself to meditation, prayer, and fasting, my soul longs for mortification, self-denial, humility and divorcement from all things of the world." "I have nothing to do," he said, "with earth, but only to labour in it honestly for God. I do not desire to live one minute for anything which earth can afford." After this high order did he pray: "Feeling somewhat of the sweetness of communion with God and the constraining force of His love, and how admirably it captivates the soul and makes all the desires and affections to centre in God, I set apart this day for secret fasting and prayer, to entreat God to direct and bless me with regard to the great work which I have in view of preaching the gospel and that the Lord would return to me and show me the light of His countenance. I had little life and power in the forenoon. Near the middle of the afternoon God enabled me to wrestle ardently in intercession for my absent friends, but just at night the Lord visited me marvellously in prayer. I think my soul was never in such agony before. I felt no restraint, for the treasures of divine grace were opened to me. I wrestled for absent friends, for the ingathering of souls, for multitudes of poor souls, and for many that I thought were the children of God, personally, in many distant places. I was in such agony from sun half an hour high till near dark that I was all over wet with sweat, but yet it seemed to me I had done nothing. O, my dear Saviour did sweat blood for poor souls! I longed for more compassion toward them. I felt still in a sweet frame, under a sense of divine love and grace, and went to bed in such a frame, with my heart set on God." It was prayer which gave to his life and ministry their marvellous power.
The men of mighty prayer are men of spiritual might. Prayers never die. Brainerd's whole life was a life of prayer. By day and by night he prayed. Before preaching and after preaching he prayed. Riding through the interminable solitudes of the forests he prayed. On his bed of straw he prayed. Retiring to the dense and lonely forests he prayed. Hour by hour, day after day, early morn and late at night, he was praying and fasting, pouring out his soul, interceding, communing with God. He was with God mightily in prayer, and God was with him mightily, and by it he being dead yet speaketh and worketh, and will speak and work till the end comes, and among the glorious ones of that glorious day he will be with the first.
Jonathan Edwards says of him: "His life shows the right way to success in the works of the ministry. He sought it as the soldier seeks victory in a siege or battle; or as a man that runs a race for a great prize. Animated with love to Christ and souls, how did he labour? Always fervently. Not only in word and doctrine, in public and in private, but in prayers by day and night, wrestling with God in secret and travailing in birth with unutterable groans, and agonies, until Christ was formed in the hearts of the people to whom he was sent. Like a true son of Jacob, he persevered in wrestling through all the darkness of the night, until the breaking of the day!"