Upon this ( ἐκ τούτου; cf. ἐξ οὗ, equivalent to qua propter). Not "from that time forwards," not a gradual thinning down or departure of some disciples, one today and another tomorrow, but a kind of rush and stampede took place.
Those who a few hours before were ready to call him their Messianic King, were entirely disenchanted. The claims of Christ were so profoundly different from what they anticipated that upon this many of his disciples went back, and walked no more with him.
The fascination those felt who had seen some of the excellences of Jesus led them to put themselves at his disposal, to wait upon him, to desert their ordinary occupations. Hence part of the phraseology of redemption was derived from the method of Christ.
Men "came" to him; they "followed" him; they "walked" with him; they could "go back," desert, forsake their Lord. These actions of his first disciples have created the vocabulary of the kingdom of God.
Christ's teaching tested as well as attracted men. There was a repellent force as well as an infinite fascination. He sifted as well as saved. The very deeds and words that broke some hearts into penitence roused impatient and angry remonstrance in others.
There is seen in this Gospel a continual departure and a deepening faith.