Matthew Poole and continuators on Acts 8:38

38 And he commanded the chariot to stand still: and they went down both into the water, both Philip and the eunuch; and he baptized him.

In hot Countries this was usual, to baptize by dipping the body in the water; and to this the Apostle alludes, when he tells the Corinthians, 1 Cor. 6.11. that they are washed, but God will have mercy, and not sacrifice; sprinkling being as effectual as washing, and as significative also, representing the sprinkling of the blood of the Paschal Lamb, of which we read, Exod. 12.3. which pre-signified the sprinkling the blood of Jesus, that Lamb of God which taketh away the sins of the world; and our hearts must by it be sprinkled from an evil conscience, Hebr. 10.22. It is not the more or the less of the outward Element, which makes the Sacraments effectual; but they are effectual onely as they are Gods appointmenst, and attended upon according to his will.