Albert Barnes on Acts 6:7

And the word of God increased. That is, the gospel was more and more successful, or became more mighty and extensive in its influence. An instance of this success is immediately added.

And a great company of the priests. A great multitude. This is recorded justly as a remarkable instance of the power of the gospel. How great this company was is not mentioned. But the number of the priests in Jerusalem was very great; and their conversion was a striking proof of the power of truth. It is probable that they had been opposed to the gospel with quite as much hostility as any other class of the Jews. And it is now mentioned, as worthy of special record, that the gospel was sufficiently mighty to humble even the proud, and haughty, and selfish, and envious priest to the foot of the cross. One design of the gospel is to evince the power of truth in subduing all classes of men; and hence in the New Testament we have the record of its having actually subdued every class to the obedience of faith. Some MSS., however, here instead of priests read Jews. And this reading is followed in the Syriac version.

Were obedient to the faith. The word faith here is evidently put for the Christian religion. Faith is one of the main requirements of the gospel, Mk 16:16, and by a figure of speech is put for the gospel itself. To become obedient to the faith, therefore, is to obey the requirements of the gospel, particularly that which requires us to believe. Comp. Rom 10:16. By the accession of the priests also no small part of the reproach would be taken away from the gospel, that it made converts only among the lower classes of the people. Comp. Jn 7:48.

(f) "the word of God" Isa 55:11, Acts 12:24, 19:20