John Chrysostom

He does not say, shall give you the Holy Ghost, but shall baptize you in the Holy Ghost, shewing in metaphor the abundance of the grace. fThis further shews, that even under the faith there is need of the will alone for justification, not of labours and toilings; and even as easy a thing as it is to be baptized, even so easy a thing it is to be changed and made better. By fire he signifies the strength of grace which cannot be overcome, and that it may be understood that He makes His own people at once like to the great and old prophets, most of the prophetic visions were by fire.