Luther didn’t come to his conclusions on justification sola fide by by himself. They were obviously rooted in prayer and a deep study of Scripture. But they also had much to do with one of his teachers in the Augustinian monastic order, Johann von Staupitz. Here’s one example where we can clearly see that Staupitz influenced Luther quite a bit (and it is an awesome quote). This is what Staupitz told Luther at one time when Luther was struggling with sin and moral failure.
“I have promised God a thousand times that I would become a better man, but I never kept my promise. From now on I am not going to make any more vows. Experience has taught me that I cannot keep them. Unless God is merciful to me for Christ’s sake and grants unto me a blessed departure, I shall not be able to stand before Him.”
Thankfully our justification, adoption, sanctification, and glorification are not based upon or grounded in our promises to God, but his to us (which are yes and amen in Christ). Staupitz knew it and he preached it to a monk named Martin Luther (and he just preached it to me!).
This great quote is found in Luther’s Commentary on Galatians 5:17 (For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. They are in conflict with each other, so that you are not to do whatever you want. [NIV2011]).