A lame man has legs; they have not been cut off, but they might as well be, for they hang limply, and serve no purpose at all. If he tries to walk on them they will not bear his weight for a moment and he will collapse, so he never makes the experiment and instead leans permanently on a crutch.
Let those who do not know God come first to Christ at the cross in repentance and faith. Let them not presume to be able to understand truth as unconverted people, as if God’s truth was just another branch of learning that they had the capacity to master in their natural state.