This remarkable claim both asserts that no one can come to Christ merely of his own volition (though he may think, sincerely, that he is doing so, not being consciously aware of all the influences God has been bringing on him in order to lead him to that decision) and also promises that none so led of the Father to Christ can ever be cast out. This involves the mystery of divine election versus human freedom. Both are true because both are taught in Scripture, but our human minds are incapable of full comprehension of this divine paradox.

Source:

KJV Defenders Study Bible, by Dr. Henry Morris, Ph.D.
Publisher: Thomas Nelson
Language: English
DEF 10 ISBN 0-529-10444-x
DEF 10-1 ISBN 0-529-10445-8