Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls. They that gladly received his word - The word ασμενως, which signifies joyfully, readily, willingly, implies that they approved of the doctrine delivered; that they were glad to hear of this way of salvation; and that they began immediately to act according to its dictates. This last sense is well expressed in a similar phrase by Josephus: when speaking of the young Israelites enticing the Midianitish women to sin, by fair speeches, he says, αἱ δε ασμενως δεξαμεναι τους λογους συνῃεσαν αυτοις, Ant. l. iv. c. 4. Then they who approved of their words consorted with them. The word is however omitted by ABCD, Coptic, Sahidic, Ethiopic, Vulgate, the Itala of the Codex Bezae, Clemens, and Chrysostom.
Were baptized - That is, in the name of Jesus, Acts 2:38, for this was the criterion of a Jew's conversion; and when a Jew had received baptism in this name he was excluded from all communication with his countrymen; and no man would have forfeited such privileges but on the fullest and clearest conviction. This baptism was a very powerful means to prevent their apostasy; they had, by receiving baptism in the name of Jesus, renounced Judaism, and all the political advantages connected with it; and they found it indispensably necessary to make the best use of that holy religion which they had received in its stead. Dr. Lightfoot has well remarked, that the Gentiles who received the Christian doctrine were baptized in the name of the Father, and the Son, and the Holy Ghost; whereas the Jewish converts, for the reasons already given, were baptized in the name of the Lord Jesus.
Were added - three thousand souls - Προσετεθησαν, They went over from one party to another. The Greek writers make use of this verb to signify that act by which cities, towns, or provinces changed their masters, and put themselves under another government. So these 3000 persons left the scribes and Pharisees, and put themselves under the teaching of the apostles, professing the Christian doctrine, and acknowledging that Christ was come, and that he who was lately crucified by the Jews was the promised and only Messiah; and in this faith they were baptized.
These 3000 were not converted under one discourse, nor in one place, nor by one person. All the apostles preached, some in one language, and some in another; and not in one house - for where was there one at that time that could hold such a multitude of people? For, out of the multitudes that heard, 3000 were converted; and if one in five was converted it must have been a very large proportion. The truth seems to by this: All the apostles preached in different, parts of the city, during the course of that day; and in that day, τῃ ἡμερᾳ εκεινῃ, 3000 converts were the fruits of the conjoint exertions of these holy men. Dr. Lightfoot thinks that the account in this place is the fulfillment of the prophecy in Psalms 110:1, etc.: The Lord said unto my Lord, sit thou on my right hand; this refers to the resurrection and ascension of Christ. Thy people shall be willing in the day of thy power, Psalms 110:3. This was the day of his power; and while the apostles proclaimed his death, resurrection, and ascension, the people came willingly in, and embraced the doctrines of Christianity.