Is Baptism necessary for Salvation?

The Bible does not say whether the thief on the cross was baptized or not. To say he was not is an assumption.

One verse says all the region of Judea and all of Jerusalem were going out to him (John the
Baptist) and were being baptized by him in the Jordan river. He could have been one of them.

Pointing out that UNLESS a person is born naturally they cannot expect to be born again of the Spirit is not necessary when speaking to someone who has obviously met the first condition.

All of the things you mention with the exception of water baptism are OT commands that pertain exclusively to the Jewish population. However, water baptism in the name of the Lord Jesus is a NT requirement and pertains to all groups of humanity as witnessed in scripture:

Acts 2:38-39 (Jews) The group did not receive the Holy Ghost the moment they believed in Jesus. However, they were told they could expect the Holy Ghost at some point.

Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost.
For the promise is unto you, and to your children, and to all that are afar off, even as many as the Lord our God shall call.
Then they that gladly received his word were baptized: and the same day there were added unto them about three thousand souls.

Acts 8:12-17 (Samaritans)
But when they believed Philip preaching the things concerning the kingdom of God, and the name of Jesus Christ, they were baptized, both men and women.
Then Simon himself believed also: and when he was baptized, he continued with Philip, and wondered, beholding the miracles and signs which were done.
Now when the apostles which were at Jerusalem heard that Samaria had received the word of God, they sent unto them Peter and John:
Who, when they were come down, prayed for them, that they might receive the Holy Ghost:
(For as yet he was fallen upon none of them: only they were baptized in the name of the Lord Jesus.)
Then laid they their hands on them, and they received the Holy Ghost.

Acts 10:43-48 (Gentiles)
43 To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins.
While Peter yet spake these words, the Holy Ghost fell on all them which heard the word.
And they of the circumcision which believed were astonished, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Ghost.
For they heard them speak with tongues, and magnify God. Then answered Peter,
Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
And he commanded them to be baptized in the name of the Lord. Then prayed they him to tarry certain days.

It's equally an assumption to claim he was baptized.

The thief knew who Jesus was, as we know because he said as much while hanging on the cross beside him.

However, if he would have been baptized it would mean the thief wouldn't have had to tell Jesus he knew who he was. Jesus would have known him.
The thief also wouldn't have asked Jesus to remember him when Jesus came into his kingdom.

And Jesus wouldn't have then said to the thief, today you will be with me in paradise.

According to some, the thief wasn't baptized and that means he wasn't really saved.

Some will balk at that though they insist that part about baptism remains true for everyone else.

However, when Jesus said we are saved by faith through God's grace, and made no condition requisite for baptism for that to be so, their argument is contrary to the facts. And reason.

If Baptism is mandatory, everyone who died and thought they were saved but weren't baptized are damned to death.

If they compromise Jesus, the living water, and his teaching that we are saved by faith by insisting it's not so unless we're baptized, Jesus can't deny himself. He can't contradict himself if he insisted we're not saved until we're also baptized. Which means he couldn't make that promise to the thief.

Jesus didn't make baptism mandatory. Others do.

All of the things you mention with the exception of water baptism are OT commands that pertain exclusively to the Jewish population.

Then why did all the Jews around the Jordan want to go get baptized by John? They weren't christians and knew nothing about Jesus. All verses that specifically mention water in the baptism involve a Jewish Christian as the one suggesting it or performing it.

The thief may have been obedient to the baptism of John, however, as seen in Paul's exchange with the 12 Ephesus disciples it did not provide the reality of the NT water baptism in Jesus' name. He actually rebaptized them in the name of the Lord Jesus, and afterward they received the Holy Ghost as well. (Acts 19:1-7) We know that being baptized in the name of the Lord is in fact water baptism as confirmed by Peter's exchange with the Gentiles in Acts 10:43-48.

"Can any man forbid water, that these should not be baptized, which have received the Holy Ghost as well as we?
And he commanded them to be baptized in the name of the Lord."

That was just another way of saying that you have to be born twice or that you have to be born again.

All of the things you mention with the exception of water baptism are OT commands that pertain exclusively to the Jewish population.

Then why did all the Jews around the Jordan want to go get baptized by John? They weren't christians and knew nothing about Jesus. All verses that specifically mention water in the baptism involve a Jewish Christian as the one suggesting it or performing it.

It's not " After they heard this ( in Acts 19: 1-7) then they went and got baptized with water again". It's "when they heard and believed about Jesus, they were instantly baptized in the name of Jesus Christ".

It was a way for them of showing God that they repented of all their sins. They don't have to show it by water baptism because God judges the hearts of man. John stated that he was told to water baptize so that he would be able to identify the one that was going to baptize with the Holy Spirit as the person upon whose head rests the Holy Spirit.

John the Baptist introduced the baptism of repentance for the remission of sin. That water baptism was later modified to include the name of the Lord Jesus in association with His death, burial and resurrection. Everyone living in the NT is required to obey the command in order for their sins to be washed away. See: Acts 2:38-42, 8:12-18, 9:17-18, 10:43-48, 19:1-7, 22:16.

Also, being baptized in the name of Jesus Christ is not the same as being baptized with water as Acts 19: 1-6 shows. They were baptized in the name of Jesus Christ through Paul's preaching about Christ not by water baptism.

That's some serious eisegesis.
Its not good practice to import personal theory into scripture against the rest of the body of text. Too many places specifically refer to water. So eliminating water just because its not specifically mentioned is error. Scripture interprets scripture. The word baptize literally means wash with water. Also the practice of the church from establishment has always included water baptism from acts to this day.

Agreed.
I dont know why there is any controversy other than heresy and sin. We have the direct words of Jesus himself, a directive to baptise.
We have Peter and Paul explain baptism and its purpose, and we have written examples of water baptism. That are quite explicit. Then after that we have the practice pf the church from then to the modern age.
Now for some reason we have those who wish to de- emphasize baptism.

The reasoning escapes me.

Read posts #454 and 455 and find out how Jesus used the word Baptism.

It's not " After they heard this ( in Acts 19: 1-7) then they went and got baptized with water again". It's "when they heard and believed about Jesus, they were instantly baptized in the name of Jesus Christ".

Read posts #454 and 455 and find out how Jesus used the word Baptism.

Been asked and challenged.
Never answered.

https://www.gotquestions.org/Godhead.html

Water baptism in the name of the Lord Jesus for the remission of one's sins was instituted on the Day of Pentecost. Obedience to it is required of everyone living in the NT in association with Jesus' death, burial and resurrection.

As stated in Hebrews 5:9, Jesus became the author of eternal salvation unto all those who obey Him. Obedience is an essential part of faith. (James 2:22-26) If you will recall it was Jesus who said he who is believes and is baptized shall be saved. He didn't say get baptized after you have been saved.

Jesus made a powerful statement that confirms the necessity of obedience:
"Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.

Therefore whosoever heareth these sayings of mine, and doeth them, I will liken him unto a wise man, which built his house upon a rock:" Matt. 21-24

I'm not sure but if this is in reference to your asking if there is a contradiction between how Jesus said to baptize and how the apostles baptized. My answer is in posts 546, 547, and 550.

Only one person meets the following criterion: "And without controversy great is the mystery of godliness: God was manifest in the flesh, justified in the Spirit, seen of angels, preached unto the Gentiles, believed on in the world, received up into glory." 1 Tim 3:16