John 6:66
“From that time many of His disciples went back, and walked no more with Him.”
Rightly has the Evangelist said, not that they “departed,” but that they “went back”; showing that they cut themselves off from any increase in virtue, and that by separating themselves they lost the faith which they had of old. But this was not the case with the twelve; wherefore He says to them,
Source: Homilies on the Gospel of John (New Advent)