Membership isn't a Doctrinal Reward
...if fulsome knowledge of the whole counsel of God were required for mere membership, one might be left wondering exactly what it is that the church is supposed to do with those who finally manage to join. Membership is not a reward for achieving a high level of doctrinal knowledge any more than a high level of personal holiness. It is the gateway to the means by which these things can become possible via the ordinary means of grace.
Carl Trueman, The Creedal Imperative (Wheaton, IL: Crossway, 2012), 172