“Because theology has to do with a knowledge of God and his relationship with his creatures. Without it, there is no knowledge of God nor can there be a relationship with him. So to be a Christian one must be a theologian” (David J. Hesselgrave, Scripture and Strategy, 36)!
Missio Dei
For the earth will be filled with the knowledge of the glory of the LORD as the waters cover the sea.
Missio Dei 
That’s the same as saying “Republicans are concerned with freedom and voter’s rights, because without these one cannot properly vote. Therefore every voter must be a Republican.”
No one else? Really? Okay, I’ll say it:
Because Christian leaders make these kinds of audacious, counterintuitive claims all the time, I can’t tell if the “right” thing to do it agree or disagree with it, so I’m just going to cut out the circuitous process of saying something, getting labeled as a pagan/heretic/secularist/puppy-kicker, and brooding in a dark room for a few weeks.
So what’s my opinion about that quotes supposed to be?
Josh,
I like cats, puppies are ok . . . were the puppies bad? Anyways, I think he is saying that if you are a follower of Christ you are a theologian because you know theology. Things like there is a God, He is sovereign and holy, He is gracious and forgives those who repent and place their confidence in His Son. You also know that man is fallen; he is not as he should be and is in need of redemption. You know that Jesus is the Son of God and Savior of the world. You may not phrase these things like John Calvin or Martin Luther but you must know these things to follow Christ. He is referencing Theology for Everyman by John H. Gerstner and explaining that theology is not reserved for the academic elite and it should not be difficult to grasp, because all who follow Christ know basic theological concepts. Hope that helps.
There were no bad puppies. I am not a puppy kicker.