It's not talking about a mutual faith of Christ, it is talking about the mutual Christian faith which is not the same thing.
If you're going to quote scripture then don't quoted out of context like you've done enough.
First, I thank my God through Jesus Christ for all of you, because your faith is being reported all over the world. 9 God, whom I serve in my spirit in preaching the gospel of his Son, is my witness how constantly I remember you 10 in my prayers at all times; and I pray that now at last by God’s will the way may be opened for me to come to you.
11 I long to see you so that I may impart to you some spiritual gift to make you strong— 12 that is, that you and I may be mutually encouraged by each other’s faith.