Luke 9:46

(non occ.) The devil lays plots of various kinds for them that love the best way of life. And if indeed by carnal allurements he can gain possession of a man's heart, He sharpens his love of pleasure; but if a man has escaped these snares, he excites in him a desire of glory, and this passion for vain-glory had seized some one of His apostles. Hence it is said, Then there arose a reasoning among them, which of them should be the greatest. For to have such thoughts, belongs to him who desires to be superior to the rest; but I think it improbable that all the disciples gave way to this weakness; and therefore suppose that the Evangelist, not to seem to lay the charge to any individual, expresses himself indefinitely, saying, that there arose a reasoning among them.

Or, because they saw Peter, James, and John, taken apart to the mount, and the keys of the kingdom of heaven promised to Peter, they were angry that these three, or Peter, should have precedence over all; or because in the payment of the tribute they saw Peter made equal to the Lord, they supposed he was to be placed before the rest. But the attentive reader will find that the question was raised among them before the payment of the penny. For in truth Matthew relates that this took place at Capernaum; but Mark says, And he came to Capernaum, and being in the house, he asked them, What was it that ye disputed among yourselves in the way? But they held their peace; for by the way they had disputed among themselves who should be the greatest. (Mat. 18:24, Mark 9:33.)

Now it seems that this feeling was excited by the circumstance of their not being able to cure the demoniac. And while they were disputing thereupon, one said, It was not owing to my weakness, but another's, that he could not be cured; and so thereby was kindled a strife among them, which was the greatest.