What is daily renewal? It is the continuation of the work of grace that the Holy Spirit began in our souls by justification through faith. It is the hearty diligence that the believing Christian exercises daily in putting off, more and more, the old man, always striving to avoid error and suppressing sin in himself. It is the earnest daily effort to put on the new man, growing in doctrine and spiritual wisdom so the Christian becomes conformed more and more to the image of Jesus Christ through words and deeds.
In this daily renewal of the Christian, he must constantly war against his weaknesses and the great corruption in himself in order that they do not rule in him. Faithless people and those with hypocritical hearts may claim that they strive to become better and more godly, but they still let sin rule over them. When the true Christian awakens in the morning, his first care, which he takes to God in prayer, is, "Oh, may I be completely faithful today!"
Whoever wants to be a Christian must be able to tell, not only of his former conversion, but also of how the work of God's grace continues daily in his heart.
CFW Walther, "God Grant It," pages 797-798
