God can be known as the God of history, the God of creation, etc. This is true. But outside of the church (not necessarily the institutional church, but the church as the people of God), there is inadequate preaching as to who God is. Who is God in the hurricane? Whoever God is in nature, it's my rather independent interpretation of what is happening that ends up being the definition of God. Certainly you won't come up with the gospel of Christ by wandering the forests.
The church is "necessary" in the sense that it was established by Christ for the clear proclamation of the Gospel, the good news. Sure, the church is, as Augustine said, a "corpus mixtum." But so was Jesus' body, fully human and fully divine. So too "the holy catholic church" is the extension of Christ's body here and now on earth, fully human, and fully divine. You can't get that anywhere else, which is what the old adage extra ecclesiam nulla sanctus attempted to say (Cyprian said it, it needs considerable commentary to be understood correctly).