A.T. Robertson Commentary John 6:66

"Upon this many of his disciples went back, and walked no more with him." — John 6:66 (ASV)

Upon this (εκ τουτου). Same idiom in 19:12. "Out of this saying or circumstance." Jesus drew the line of cleavage between the true and the false believers.

Went back (απηλθον εις τα οπισω). Aorist (ingressive) active indicative of απερχομα with εις τα οπισω, "to the rear" (the behind things) as in 18:6.

Walked no more with him (ουκετ μετ' αυτου περιεπατουν). Imperfect active of περιπατεω. The crisis had come. These half-hearted seekers after the loaves and fishes and political power turned abruptly from Jesus, walked out of the synagogue with a deal of bluster and were walking with Jesus no more. Jesus had completely disillusioned these hungry camp-followers who did not care for spiritual manna that consisted in intimate appropriation of the life of Jesus as God's Son.