John Calvin on Acts 8:35

35. Philip, opening his mouth. To open the mouth is taken in Scripture for, to begin a long speech concerning some grave and weighty matter. Therefore Luke’s meaning is, that Philip began to intreat [discourse] of Christ, as it were, with full mouth. He saith that he began with this prophecy, because there is no one which depainteth out Christ more lively; “Clarius,” more clearly. and it was then brought “Commode,” conveniently, omitted. to his hand. Therefore, after that Philip had showed, by the prophet’s words, after what sort Christ should come, and what was to be hoped for at his hands, he conferred the thing itself afterward, that the eunuch might know that that Christ which was promised was already revealed and given, and that he might understand his power. Where we translate it, that he preached Christ, Luke saith that he preached the gospel. The sense is, that he taught that of Christ which he uttered in his gospel himself, and commanded to be taught; whereby we gather, that when Christ is known, we have the sum of the gospel.

Acts 8:36-40

36. And as they went on the way, they came to a water. And the eunuch said, Lo, here is water, what letteth me to be baptized? 37. And Philip said, If thou believest with all thy heart, thou mayest. He answering, said, I believe that Jesus Christ is the Son of God. 38. Then he commanded the chariot to be stayed, and they went both down into the water; to wit, Philip and the eunuch, and he baptized him. 39. And when they were come out of the water, the Spirit of the Lord caught away Philip, and the eunuch saw him no more. Therefore, he went on in his way rejoicing. 40. But Philip was found at Azotus; and, going on his journey, he preached the gospel to all cities, until he came to Cesarea.