This prayer comes from the book Prayers of the Reformers compiled by Clyde Manschreck. It was written by John Calvin.
“Grant, almighty God, since thou dost try the faith of thy people by many tests that they may obtain strength from the unconquered fortitude of thy Holy Spirit. May we constantly march under thy standard, even to the end, and never succumb to any temptation. May we join intelligence with zeal in building up thy church. As each of us is endowed with superior gifts so may he strive for the edification of his brethren with greater boldness, manliness and fervor, while he endeavors to add numbers to the cause. And should the number diminish, yet may some seed always remain, until abundant produce shall flow forth from it, and such fruitfulness arise as shall cause thy name to be glorified throughout the world, in Jesus Christ our Lord. Amen.”