And they were astonished at his doctrine The meaning of the Evangelists is, that the power of the Spirit shone in the preaching [1] of Christ with such brightness, as to extort admiration even from irreligious and cold hearers. Luke says, that his discourse was accompanied with power, that is, full of majesty. Mark expresses it more fully, by adding a contrast, that it was unlike the manner of teaching of the Scribes As they were false expounders of Scripture, their doctrine was literal and dead, breathed nothing of the power of the Spirit, and was utterly destitute of majesty. The same kind of coldness may be now observed in the speculative theology of Popery. Those masters do indeed thunder out whatever they think proper in a sufficiently magisterial style; but as their manner of discoursing about divine things is so profane, that their controversies exhibit no traces of religion, what they bring forward is all affectation and mere drivelling: for the declaration of the Apostle Paul holds true, that the kingdom of God is not in word, but in power, (1-Corinthians 4:20.) In short, the Evangelists mean that, while the manner of teaching, which then prevailed, was so greatly degenerated and so extremely corrupted, that it did not impress the minds of men with any reverence for God, the preaching of Christ was eminently distinguished by the divine power of the Spirit, which procured for him the respect of his hearers. This is the power, or rather the majesty and authority, at which the people were astonished.

Footnotes

1 - "En la facon d'enseigner de Jesus Christ;" -- "in Jesus Christ's manner of teaching."

His word was with power - Εν εξουσιᾳ, With authority. He assumed the tone and manner of a new Lawgiver; and uttered all his doctrines, not in the way of exhortation or advice, but in the form of precepts and commands, the unction of the Holy Spirit accompanying all he said. See on Mark 1:22 (note).

And they were astonished at his doctrine,.... At the matter of it, as well as the manner in which it was delivered, it being so different from the Scribes and Pharisees, they had been used to:
for his word was with power: he spake with great fervency, majesty, and authority, and not with coldness and indifference, and dependence on the sense and authority of others, as their teachers did; and besides, such power went along with the word, that it reached their hearts; and as the Persic version renders it, "he penetrated them with it"; and he also confirmed it by powerful operations, by miraculous works, such as casting out devils, and healing diseases, of which an account follows.