John Calvin on John 12:4

4. One of his disciples, therefore, saith. Next follows the murmuring of Judas, which Matthew (Matthew 16:8) attributes to the disciples indiscriminately, and Mark (Mark 14:4) to some of them; but it is customary in Scripture to apply to many, by way of synecdoche, what belongs to one or to a few. Yet I think it is probable, that the murmuring proceeded from Judas alone, and that the rest were induced to give him their assent, as murmurings, by fanning a flame, easily kindle in us a variety of dispositions; and more especially, as we are too prone to form unfavorable judgments, slanders are readily embraced by us. But the credulity which the Spirit of God reproves in the Apostles is a warning to us not to be too easy and credulous in listening to calumnious statements.