Prepositions are important little words and can certainly change the meaning of a phrase.
In this case, though, the title is correct. The Gospel of Life is what pastors are to proclaim. After preaching a sermon for a church centennial celebration, former Lutheran Hour speaker Dr. Oswald Hoffmann, received one of the greatest compliments a preacher could receive. That is what pastors, Lutheran pastors, are called to do. They are not called to spew nice sounding words into the air.