And Philip said - This was stated by Philip as the proper qualification for making a profession of religion. The terms are:
(1) "Faith," that is, a reception of Jesus as a Saviour; yielding the mind to the proper influences of the truths of redemption. See the notes on Mark 16:16.
(2) there is required not merely the assent of the understanding, but a surrender of the "heart, the will, the affections," to the truth of the gospel. As these were the proper qualifications then, so they are now. Nothing less is required; and nothing but this can constitute a proper qualification for the Lord's Supper.
I believe - This profession is more than a professed belief that Jesus was "the Messiah." The name "Christ" implies that. "I believe that Jesus the Messiah is the Son of God." He professed his belief that he was the "Son of God" - showing either that he had before supposed that the Messiah "would be" the Son of God, or that Philip had instructed him on that point. It was natural for Philip, in discoursing on the humiliation and poverty of Jesus, to add also that he sustained a higher rank of being than a man, and was the Son of God. What precise ideas the eunuch attached to this expression cannot be now determined. This verse is missing in a very large number of manuscripts (Mill), and has been rejected by many of the ablest critics. It is also omitted in the Syriac and Ethiopic versions. It is not easy to conceive why it has been omitted in almost all the Greek mss. unless it is spurious. If it was not in the original copy of the Acts , it was probably inserted by some early transcriber, and was deemed so important to the connection, to show that the eunuch was not admitted hastily to baptism, that it was afterward retained. It contains, however, an important truth, elsewhere abundantly taught in the Scriptures, that "faith" is necessary to a proper profession of religion.

I believe that Jesus Christ is the Son of God - He believed that Jesus, whom Philip preached to him, was The Christ or Messiah, and consequently the Son of God.
This whole verse is omitted by ABCG, several others of the first authority, Erpen's edit. of the Arabic, the Syriac, the Coptic, Sahidic, Ethiopic, and some of the Slavonic: almost all the critics declare against it as spurious. Griesbach has left it out of the text; and Professor White in his Crisews says, "Hic versus certissime delendus," this verse, most assuredly, should be blotted out. It is found in E, several others of minor importance, and in the Vulgate and Arabic. In those MSS. where it is extant it exists in a variety of forms, though the sense is the same.

(13) And Philip said, If thou believest with all thine heart, thou mayest. And he answered and said, (n) I believe that Jesus Christ is the Son of God.
(13) Profession of faith is required of those being baptized, and therefore it is evident that we are not first ingrafted into Christ when we are baptized, but are already ingrafted, and then are baptized. (Ed.)
(n) The sum of the confession which is necessary for baptism.

And Philip said, if thou believest with all thine heart, thou mayest,.... Intimating, that if he did not believe, he had no right to that ordinance; though he was a proselyte to the Jewish religion, a serious and devout man, and was employed in a religious way, when Philip came up to him, and was very desirous of being instructed in the knowledge of divine things; and yet notwithstanding all this, he had no right to the ordinance of baptism, unless he had faith in Christ, and made a profession of it; nor would Philip administer it to him without it; from whence it appears, that faith in Christ, and a profession of it, are necessary prerequisites to baptism: and this faith should not be a mere historical and temporary faith, nor a feigned one, but a believing in Christ with the heart unto righteousness; or such a faith by which a soul relinquishes its own righteousness, and looks and goes unto Christ for righteousness, life, and salvation, and rests and relies upon him for them; and it should be a believing in him with the whole heart, which does not design a strong faith, or a full assurance of faith, but an hearty, sincere, and unfeigned one, though it may be but weak, and very imperfect. And that this is necessary to baptism is manifest, because without this it is impossible to please God; nor can submission and obedience to it be acceptable to him: nor indeed can the ordinance be grateful and pleasing to unbelievers; for though it is a command that is not grievous, and a yoke that is easy, yet it is only so to them that believe; nor can any other see to the end of this ordinance, or behold the burial, and resurrection of Christ represented by it, or be baptized into his death, and partake of the benefits of it; and besides, whatsoever is not of faith is sin.
And he answered and said, I believe that Jesus Christ is the Son of God: which though a short, is a very comprehensive summary of the articles of faith respecting the person, offices, and grace of Christ; as that he is a divine person, truly and properly God, the only begotten of the Father, of the same nature with him, and equal to him; that he existed from all eternity, as a divine person with him, and distinct from him; and that he is the Christ, the anointed of God, to be prophet, priest, and King; and is Jesus, the only Saviour of lost sinners, in whom he trusted and depended alone for righteousness, life, and salvation. This whole verse is wanting in the Alexandrian copy, and in five of Beza's copies, and in the Syriac and Ethiopic versions; but stands in the Vulgate Latin and Arabic versions, and in the Complutensian edition; and, as Beza observes, ought by no means to be expunged, since it contains so clear a confession of faith required of persons to be baptized, which was used in the truly apostolic times.

If thou believest, etc.? This verse is omitted in the Revision. It is not found in the oldest extant manuscripts, but was certainly in manuscripts older than any now extant. It is referred to by IrenÃ&brvbr;us in the second century, and by Augustine in the fourth. Whether written by Luke or not, it shows that the custom of the early church was to require such a confession of faith.
With all thine heart. A living faith must seize upon and control the heart.