In Romans 1:11-12, Paul is writing to the believers in Rome and says he wants to "impart a Spiritual gift" unto them so that, “to the end they might be established” and, "that he may be comforted in the mutual faith of one another".
The "mutual faith" here is referring to the fact that they both believe in what Jesus did for them at the cross, the Gospel; and the particular "gift" he wants to impart, is to impart a further and deeper understanding of the cross. Hence, being "comforted" in the same, or mutual "faith".
This is evident in Romans 1:16-17, when Paul "imparts" a reminder to these BELIEVERS to continue their walk with God by faith in the Gospel, the cross of Jesus (I emphasize "BELIEVERS" because a lot of people imply that these verses are to get people "saved"). The exhortation is to LIVE by the same "faith" that got them saved because the righteousness of God is being "revealed from faith to faith"; meaning from initially believing in His cross, to continue on by trusting in His cross.
After discussing God's glorious "justification" for the first four chapters, in chapters five, six, seven, and eight Paul transitions into the topic of "sanctification" by this same "faith"... Thats good news for you and me! This means that "He Who began a good work in you, is faithful to perform it", and the way He is performing it, is the same way He performed "justification", by faith in His cross. I'll say that's comforting!!!
Just like we couldn't perform our own justification, we can't anymore perform the perfecting of ourselves, or sanctification. The good, great, and comforting news is that you don't have to try!!! Purpose only (and I mean PURPOSE) to keep you faith (trust, reliance, dependency) in what Jesus did for you, and this will be God's channel or avenue to do in you, what you could never do in yourself. Just like "justification"...
Hallelujah!!!