In the Scriptures there is a long history of baptism, and each time baptism resembled death and resurrection. In each instance of baptism, God symbolically raised the baptized to new life; in so doing, He established a people who belonged to Him.
There were three major baptisms in the Old Testament. The first baptism we see in Scripture is the Flood. Out of the waters that threatened to destroy everyone, God rescued Noah and his family, made a covenant with them and declared them to be His people. The second baptism we read about is the Exodus. After God rescued the Israelites from slavery in Egypt, He led them to the sea where they would have drowned without His intervention. But God led them through the waters to new life on the other side, and again, He made a covenant and declared them His people. We see a third baptism as the Israelites finally prepared to enter the long-awaited Promised Land. Somehow they had to cross the Jordan River in order to enter the Promised Land, so God held back the waters until He’d led them safely to the other side. There they received what God had promised, and once again, He declared them to be His people.
So baptism was always something God initiated — He blessed people with His presence and promises, not because they deserved it, but as the free gift of grace from a God who gives us what we don't deserve.
Ever since, whenever anyone wanted to join the community who worshiped the one true living God, Jews insisted that they be baptized like they were. This symbolized that they were taking on a new identity of people whose old identities had been drowned in death and then raised to new life — born again as God's chosen people.
As we enter the New Testament, John the Baptist is the first person we see baptizing; scandalously, he baptized Jews too. In so doing, he was reminding them that its not enough to simply be a born into a community that belongs to God; each of us must individually enter into the identity and inheritance shared by all God's people.
Ever since, whenever new people have come to worship the living God who was revealed in Jesus, they are baptized as a visual expression of the new life that they have received in Jesus. As they descend into the water, we remember that our old identity, sins and ambitions die with Christ — nailed to His cross. As they emerge from the water, we remember that they’ve been born again into new life, into the family of the global church, and into an inheritance prepared for them that will never perish, spoil, or fade. This is not an achievement of any kind; it's a gift we don't deserve, but which we receive because in His grace, God has called us His very own children.