Water Baptism is symbolic of cleansing and rebirth. The ancient’s understanding was that some sort of spiritually cleansing followed the act of physical cleansing — washing or bathing.
My Lord said that we need to be “born again”: that we are born once of the flesh (born of our mother) but that we need to be born of the Spirit (Holy Spirit).
Being born again is a spiritual rebirth. We need to repent and have our sins washed away, cleansed by the Word of God, and after which the Holy Spirit comes to abide in us. That comes from turning to Yeshua (The Word) and reading the Bible (the Word). The act of water immersion adult baptism is important, but it is symbolic of the inner change. The inner change is what is needed to be saved.
Yeshua, in one, fulfilled the Law (of the Old Testament), ushering in the era of the Holy Spirit. Born-again means to be born of the Spirit. You can be physically immersed in water and still not have received the Holy Ghost (clearly discussed by Paul in Acts of the Apostles).
Literal water immersion baptism is the outward symbolism of the inward change. Symbolism is important as a reaffirmation of your purpose and re-commitment, and as an outward sign to the world of the reason of your faith. The critical point is the spiritual rebirth: turning from sin and turning to God, through His Son, Yeshua.