It does not appear from the text that they knew who Jesus was.What those disciples of John had not received yet was Holy Spirit manifestation, Holy Spirit baptism. This they received when Paul laid hands on them. It does not say in the context that they were unregenerates or unbelievers etc. They were believers in the Messias, but were without Holy Spirit baptism.
Acts 19:2-5 he said to them, "Did you receive the Holy Spirit when you believed?" So they said to him, "We have not so much as heard whether there is a Holy Spirit." 3 And he said to them, "Into what then were you baptized?" So they said, "Into John's baptism." 4 Then Paul said, "John indeed baptized with a baptism of repentance, saying to the people that they should believe on Him who would come after him, that is, on Christ Jesus." 5 When they heard this, they were baptized in the name of the Lord Jesus.
Paul assumed that they were believers when he addressed them, but Paul had to tell them about Christ. There are various ways of reading the aorist participle, but it seems most likely to me that we should read it as most versions do, as 'when they heard this'. It does not say after they heard this or that when they heard this they went and found a lake somewhere, but when they they heard this they were all baptized in the name of the Lord Jesus. How could he have immersed them all at once while he said this?
It seems perfectly fitting that while explaining to them what John's baptism pointed to, they should receive the baptism of Jesus.
Matthew 3:11 "I indeed baptize you with water unto repentance, but He who is coming after me is mightier than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire.
Please explain what you believe it means.Look in the Greek text, verse 2, and learn what "pneuma hagion" (2 x) without the article means here.
But that's one of the things that baptism is a picture of and the word baptism is often used interchangably with it.Also it does not say what you stated that upon hearing Paul's words they were baptized by regeneration.
Titus 3:5 He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit,
It does not say they received Holy Spirit baptism, it says they received the gift of the Holy Spirit. The Bible does not speak of a separate baptism of the Holy Spirit.And after this Paul laid hands on them and at this point they received Holy Spirit baptism,
The verb form of the word is used in Acts 17:23 to speak of those who worship an idol. "eusebes" is only found a couple of times in the Bible, it does not occur often enough to think that each time it occurs it must be referring to a regenerate person. Most translations translate it as devout in this passage, which is probably the best way to go. The word is used in a great deal of Greek literature to speak of people who diligently carried out sacrifices to their gods.The KJV says "devout", the Greek has "eusebês". This is a word which in the NT is never, as far as I know, used with reference to unregenerate people.
Sola Gratia,
WildBoar