John Gill

Because that by reason of him,.... Of the miracle which was wrought upon him, in raising him from the dead, of which he was a living and an abiding witness: many of the Jews went away; not from Jerusalem only, but from the chief priests and Pharisees, and the rest of the Jews, that combined against Christ; they withdrew themselves from their party, and deserted them: and believed on Jesus; as the Messiah; so that they found their interest was decreasing and weakening every day, and that those on the side of Christ were increasing; and this they could not bear, and therefore consulted to take away the life of Lazarus, as well as Jesus; who they imagined, as long as he lived, would be a means of inducing persons to believe in Jesus as the Messiah: whereas if he was dead, the fact would be forgotten, or be more easily denied.