Note 9 at Joh 6:45: The Old Testament prophets prophesied of a New Covenant where we would all be taught of God (Isa 54:13 and Jer 31:34). This is speaking of revelation knowledge (see note 1 at Lu 2:26) that comes from within through our spirits. Under the Old Covenant (Mosaic), God dealt with the Jews through the outer man. He did this because an Old Covenant person (who was not born again - see note 6 at Joh 3:10) could not perceive the spiritual truths revealed by the Spirit in the New Covenant (1Co 2:14). This difference between the Old and New Covenants is the reason why there had to be two covenants.

The Old Testament people were comparable to children in their ability to grasp spiritual truth (Mt 11:11, Ro 16:25, 1Co 2:14, Col 1:26-27, and 1Pe 1:10-11). It's impossible to explain spiritual truth to young children, and yet children must be restrained from submitting to evil. So the Word of God teaches us to use the "rod of correction" (Pr 13:24, 19:18, and 22:15). Children may not understand resisting the devil, yet when the devil tries to entice them to steal, they will say "No!" because they fear they will get the rod if they do steal.

Likewise, Old Testament saints were restrained from sin by a fear of the wrath and punishment of God. This curbed sin, but it also hindered them from receiving the goodness and love of God (1Jo 4:18).

Under the New Testament, which Jesus was speaking of in this verse, the punishment for our sins was laid on Him (2Co 5:21 and 1Pe 2:24). We don't serve God out of fear of punishment, as when we were "children" under the Law (Ga 3:23-26), but we serve Him out of love because He has sent the Spirit of His Son into our hearts (Ga 4:1-6) making us His sons and daughters. We serve Him because our nature has been changed through the new birth (see note 2 at Joh 3:3). We are now all taught of God through the indwelling presence of Christ.