Faith and grace are nothing new. The people of the OT were/are saved the same way we are .... through Christ ... their faith in the promise of the Messiah to come. Baptism was not required then and is not required now to receive salvation.
1 Peter 3:18 (RSV) For Christ also
died for sins once for all (all sinners, past, present & future),
the righteous for the unrighteous, that he might bring us to God, being put to death in the flesh but made alive in the spirit;
By baptism (Gentile and Jew alike) we confess our faith in the death and resurrection of Jesus Christ, and testify of our death to sin and of our purpose to walk in newness of life. Thus we acknowledge Christ as Lord and Saviour, become His people, and are received as members by His church (believers in Christ). Baptism is a symbol of our union with Christ, the forgiveness of our sins, and our reception of the Holy Spirit. It is by immersion in water and is contingent on an affirmation of faith in Jesus and evidence of repentance of sin. It follows instruction in the Holy Scriptures and acceptance of their teachings. (Matt. 28:19, 20; Acts 2:38; 16:30-33; 22:16; Rom. 6:1-6; Gal. 3:27; Col. 2:12, 13.)
The teaching is highly nuanced and we can lose sight of the central theme very easily if we are not careful.
The benefits of baptism is access to edification from God is unlocked :
1 Corinthians 10
3and all ate the same spiritual food; 4and all drank the same spiritual drink, for they were drinking from a spiritual rock which followed them; and the rock was Christ.
Baptism isn't required to receive the benefits of baptism. Abraham was baptized, and he was edified by seeing God's great work in delivering him from Abhimelec and Pharaoh. His faith was sufficiently strong for God to confirm his election, by the time he was asked to sacrifice Isaac.
Israel was baptized, and she was edified by seeing God's great work in delivering him from Pharaoh. God continued to edify Israel, by creating evil, calamities and then delivering. But it off a million Israelites over twenty, only Joshua benefited from the building up:
1 Corinthians 10
5Nevertheless, God was not pleased with most of them; their bodies were scattered in the wilderness.
Psalms 106
13But they quickly forgot his deeds
and did not wait for his counsel.
14They were overwhelmed with craving in the wilderness,
so God tested them in the wasteland.
15God granted them their request,
but sent leanness into their lives.
John began baptising because it was revealed to him that the Rock was being given. His baptism enabled people to recognise the Messiah, because it modeled the drinking from the Rock theme:
John 1
19This was John’s testimony when the Jewish leadersp sent priests and descendants of Levi to him from Jerusalem to ask him, “Who are you?”
20He spoke openly and, remaining true to himself,q admitted, “I am not the Messiah.”r
21So they asked him, “Well then, are you Elijah?”
Johns said, “I am not.”
“Are you the Prophet?”
He answered, “No.”
22“Who are you?” they asked him. “We must give an answer to those who sent us. What do you say about yourself?”
23He replied, “I am
‘…a voice crying out in the wilderness,
“Prepare the Lord’st highway,”’u
as the prophet Isaiah said.”
24Now those menv had been sent from the Pharisees. 25They asked him, “Why, then, are you baptizing if you are not the Messiah,w or Elijah, or the Prophet?”
26John answered them, “I am baptizing withx water, but among you stands a man whom you do not know, 27the one who is coming after me, whose sandal straps I am not worthy to untie.”sandal straps I am not worthy to untie.” 28This happened in Bethanyy on the other sidez of the Jordan, where John was baptizing.
29The next day, Johnaa saw Jesus coming toward him and said, “Look, the Lamb of God who takes away the sin of the world! 30This is the one about whom I said, ‘After me comes a man who ranks above me, because he existed before me.’ 31I didn’t recognize him, but I came baptizing withbb water so that he might be revealed to Israel.”
32John also testified, “I saw the Spirit coming down from heaven like a dove, and it remained on him. 33I didn’t recognize him, but the one who sent me to baptize withcc water told me, ‘The person on whom you see the Spirit descending and remaining is the one who baptizes withdd the Holy Spirit.’ 34I have seen this and have testified that this is the Sonee of God.”
Although Abraham and Israel were not physically baptized, they nevertheless received edification since they had actually experienced spiritual baptism,
thus qualified for it, since they were unhappy with Egypt:
Hebrews 11
13All these people died having faith. They did not receive the things that were promised, yet they saw them in the distant future and welcomed them, acknowledging that they were strangers and foreigners on earth. 14For people who say such things make it clear that they are looking for a country of their own. 15If they had been thinking about what they had left behind, they would have had an opportunity to go back. 16Instead, they were longing for a better country, that is, a heavenly one. That is why God is not ashamed to be called their God, because he has prepared a city for them.
1 Peter 2
11Beloved, I urge you, as foreigners and exiles, to abstain from the desires of the flesh, which war against your soul.
So if a person is unhappy, feels alienated by the ways of the world, and cries out to God, God will unlock access to edification.
Physical baptism was introduced to clarify what the process was about.