“And the LORD said unto him [Moses], Who hath made man’s mouth? or who maketh the dumb, or deaf, or the seeing, or the blind? have not I the LORD?” (Exo 4:11)
Note that the verse says, “who makes the mute or the deaf, or the seeing or the blind?” Who makes those people? Who makes mute people; who makes deaf people; who makes blind people? It does not say “who makes people mute who would otherwise speak or who makes people blind who would otherwise see?” God takes responsibility for making people but not for making them blind etc – that is the work of the enemy.
The context of this passage is important to consider. Moses was trying to be excused from God’s assignment to him to request that Pharaoh release the Israelites from slavery. Moses reply was:
“… O my Lord, I am not eloquent, neither heretofore, nor since thou hast spoken unto thy servant: but I am slow of speech, and of a slow tongue.” (Exo 4:10)
In Exodus 4:11 God was, of course, countering Moses excuse saying He has made all people and is able to overcome such defects and then proposes how He would deal with the defect Moses was claiming as an excuse – and Moses was not even mute. His question to Moses could be understood as a rhetorical question. The answer being that if God could make people in the first place he could certainly fix any defects and enable them to function fully.
We should always interpret Old Testament passages, especially the more difficult ones, in the light of the New Testament, the later and greater revelation (recognizing that truth is progressive). Jesus claimed to be the full revelation of His Father and any understandings must be consistent with the character He portrayed. He consistently healed diseased minds and bodies. The interpretation of Exodus 4:11 cannot contradict Jesus’ example or teaching.