Albert Barnes on Acts 8:38

And they went down both into the water. This passage has been made the subject of much discussion on the subject of baptism. It has been adduced in proof of the necessity of immersion. It is not proposed to enter into that subject here. Mt 3:6. It maybe remarked here, that the preposition εις, translated here "into," does not of necessity mean that. Its meaning would be as well expressed by "to," or "unto," or, as we should say, "they went to the water," without meaning to determine whether they went into it or not. Out of twenty-six significations which Schleusner has given the word, this is one. Jn 11:38: "Jesus therefore groaning in himself, cometh to εις the grave "--assuredly not into the grave. Lk 11:49: I send them prophets. Greek, I send to εις them prophets" --to them, not into them. Comp. Rom 2:4; 1Cor 14:36, Mt 12:41: "They repented at εις the preaching of Jonas"--not into his preaching, Jn 4:5: "Then cometh he to εις a city of Samaria," that is, near to it; for the context shows that he had not yet entered into it. Comp. Jn 4:6,8 Jn 21:4: "Jesus stood on εις the shore;" that is, not in, but near the shore. These passages show that the word does not necessarily mean that they entered into the water; but

(1.) if it did, it does not necessarily follow that the eunuch was immersed. There might be various ways of baptizing, even after they were in the water, besides immersing. Sprinkling or pouring might be performed there as well as elsewhere.

(2.) It is incumbent on those who maintain that immersion is the only valid mode of baptism, to prove that this passage cannot possibly mean anything else, and that there was no other mode practised by the apostles.

(3.) It would be still incumbent to show that if this were the common and even the only mode then, in a warm climate, etc., that it is indispensable that this mode should be practised everywhere else. No such positive command can be adduced. And it follows, therefore, that it cannot be proved that immersion is the only lawful mode of baptism. Mt 3:6.