Augustine of Hippo — as excerpted in the Catena Aurea on John 6:41-46

“(Tr. xxvi) He took man’s flesh upon Him, but not after the manner of men; for, His Father being in heaven, He chose a mother upon earth, and was born of her without a father. The answer to the murmurers next follows: Jesus therefore answered and said unto them, Murmur not among yourselves; as if to say, I know why ye hunger not after this bread, and so cannot understand it, and do not seek it: No man can come to Me except the Father who hath sent Me draw him. This is the doctrine of grace: none cometh, except he be drawn. But whom the Father draws, and whom not, and why He draws one, and not another, presume not to decide, if thou wouldest avoid falling into error. Take the doctrine as it is given thee: and, if thou art not drawn, pray that thou mayest be.”