The Ethiopian eunuch of Acts 8 was either a diaspora Jew (a Jew who lived outside the land of Israel), or he was an Ethiopian proselyte to "Judaism" (a black convert to Judaism). (I personally believe the second). Historically speaking, this eunuch, or someone like him, was the one who brought Christianity into Ethiopia. Therefore this incident in Acts 8 is the incident in which the word of God was brought to the Ethiopians for the first time.
ACTS 8:26 And the angel of the Lord spake unto Philip, saying, Arise, and go toward the south unto the way that goeth down from Jerusalem unto Gaza, which is desert.
ACTS 8:27 And he arose and went: and, behold, a man of Ethiopia, an eunuch of great authority under Candace queen of the Ethiopians, who had the charge of all her treasure, and had come to Jerusalem for to worship,
ACTS 8:28 Was returning, and sitting in his chariot read Esaias the prophet.
ACTS 8:35 Then Philip opened his mouth, and began at the same scripture, and preached unto him Jesus.
ACTS 8:36 And as they went on their way, they came unto a certain water: and the eunuch said, See, here is water; what doth hinder me to be baptized?
ACTS 8:37 And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God.
ACTS 8:38 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.
ACTS 8:39 And when they were come up out of the water, the Spirit of the Lord caught away Philip, that the eunuch saw him no more: and he went on his way rejoicing.
10.1.1 As with the first time with the Jews (and all humanity, for that matter), and as with the first time with the Samaritans (the semi–Jews), so too with the first time with the Ethiopians: baptism is specifically mentioned. (Acts 8:36,38.)
10.1.2 Water baptism is part of the gospel of Jesus Christ. Today, many churches say "We preach Jesus," but they do not teach that baptism is for the forgiveness of sins (Acts 2:38), and thus is required for salvation (Mark 16:16). Here, Philip "preached unto him Jesus." We know that at some point of his "preaching Jesus" that baptism must have been taught, for it was the eunuch—not Philip—who said: "Here is water; what doth hinder me to be baptized" in Acts 8:36. Preaching baptism is perfectly consistent with what has been written up to this point anyway, for Jesus Christ preached it before His death, and commanded it before His ascension into heaven, and the apostle Peter likewise preached it as part of the gospel of Jesus Christ.
10.1.3 Belief in Jesus Christ is a prerequisite for baptism. Acts 8:36-37, demonstrates this. When the eunuch asked if he could be baptized, Philip answered:
ACTS 8:37 And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, I believe that Jesus Christ is the Son of God.
Such teaching is perfectly consistent with what Christ taught:
MARK 16:16 He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
Without faith, baptism is not accepted.
It's not so much the act of immersion in water that saves, but rather, it's the obedience to the commandment. Why obey this? The reason would be something like: "Jesus said.., I believed His word.., therefore I did as He said." Peter was pretty specific when he later wrote:
1 PETER 3:21 The like figure whereunto even baptism doth also now save us (not the putting away of the filth of the flesh, but the answer of a good conscience toward God,) by the resurrection of Jesus Christ:
1Peter 3:20-21 will be examined later in more detail, in section 21.
10.1.4 Baptism is not an "outward sign of an inward change," nor is it to "publicly identify the believer with Jesus Christ."
If you recall, Jesus said that "one jot or one tittle shall in no wise pass from the law, till all be fulfilled" (Matthew 5:18). This says something about the importance of every word of scripture. From this we can conclude that if this Ethiopian were accompanied by an entourage, then it would have been mentioned in the "jots and tittles" of Acts 8. Otherwise, if they were accompanied by others, and if it were significant, then it would be mentioned. There is no mention of any entourage accompanying this eunuch. Therefore, if there were others present, then their presence was not important enough to even mention, or, there were simply no other people there at all. If baptism were for the purpose of "publicly identifying the believer with Jesus Christ," then the presence of an entourage would then be significant.
The way Acts 8:26-38 is actually written, either Philip and this eunuch are the only two people there, or, if there were others present, their presence with Philip and the eunuch is irrelevant (because they're not mentioned). Therefore, this baptism of the eunuch was not done for the purpose of being public. Furthermore, Jesus Christ said not to do such things for the purpose of being seen by other people:
MATTHEW 6:1 Take heed that ye do not your alms before men, to be seen of them: otherwise ye have no reward of your Father which is in heaven.
10.1.5 This eunuch never spoke any kind of "tongues." There are people who teach that you have to speak in tongues to be saved. (Actually, they say that in addition to water baptism, you must also receive the gift of the Holy Ghost to be saved, and that speaking in tongues is always the initial evidence of this.)
ACTS 8:39 And when they were come up out of the water, the Spirit of the Lord caught away Philip, that the eunuch saw him no more: and he went on his way rejoicing.
This ethiopian eunuch never spoke in "tongues." He "went on his way rejoicing," but he never spoke with tongues. This is perfectly consistent with the precedent-setting example of the day of Pentecost. The three thousand who were "added unto them" (saved) at Acts 2:41 likewise did not speak in tongues.
Furthermore, when Jesus Himself was baptized..."to fulfill all righteousness," He never spoke with tongues, even though the heavens were opened to Him, and the Holy Ghost came upon Him (as a dove). He never spoke with tongues, however. (cf. section 1, above.)
10.1.6 The Ethiopian eunuch was fully immersed in water—he was not "sprinkled."
ACTS 8:38 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.
ACTS 8:39 And when they were come up out of the water, the Spirit of the Lord caught away Philip, that the eunuch saw him no more: and he went on his way rejoicing.
If "baptism" meant either "sprinkling" or "pouring," then there would be no reason to go more than ankle-deep in the water. In fact, there would be no reason to enter the water at all: merely a handful of water would be sufficient.
As we have just read, however, both Philip and the eunuch "went down both into the water," where Philip baptized him. After the eunuch's baptism, the two of them "were come up out of the water". Philip wasn't being baptized, the eunuch was. The only reason why Philip would go into the water with the eunuch is that they needed water deep enough to fully immerse the eunuch.
See section 2 above, for the definition of the word "baptize." Acts 8:38 says that Philip "baptized" (immersed) the eunuch he did not "rhantize" (sprinkle) him.
10.1.7 Being in a desert is no excuse for not obeying the commandment of water baptism.
ACTS 8:26 And the angel of the Lord spake unto Philip, saying, Arise, and go toward the south unto the way that goeth down from Jerusalem unto Gaza, which is desert.
ACTS 8:36 And as they went on their way, they came unto a certain water: and the eunuch said, See, here is water; what doth hinder me to be baptized?
Philip started out in Samaria (which is quite a distance north of Jerusalem), and was specifically told by God to go to the road that goes to Gaza, "which is desert" (Acts 8:26). Philip and eunuch were at-or-near Gaza when the eunuch was baptized. Gaza is a desert place, and there is no water in the desert (that's why it's a desert). Nevertheless, they came to a "certain water" (Acts 8:36).
From these observations we learn that if you are to be saved, God will make a way for all these things to happen! If you are to so much as even hear the word of God (John 6:44, 1John 4:19, John 3:27, etc.), then God will send someone to you, or He will arrange your circumstances so that your paths will meet. If you are to believe, and be baptized, then God will make a way for this to happen (for even though Gaza is desert, they came upon "a certain water" anyway). Even as it is written:
2 PETER 3:9 The Lord is not slack concerning his promise, as some men count slackness; but is longsuffering to us-ward, not willing that any should perish, but that all should come to repentance.