The Bible states that "in Adam, all died".
Like the president of a country who, on behalf of his people, declares war on an other country, Adam fell in emnity with God. As Adam fell in enmity with God, so did we all. Thus each person is born at enmity with God and in desperate need of a Savior. The Bible says "
through one transgression there resulted condemnation to all men" and "through the one man's disobedience the many were made sinners". From Adam's one transgression all men are justly condemned.
That is, God selected Adam to represent us all in the Garden. Adam did just what we all would have done and so we are all condemned. Just as the most innocent looking child born in a country at war is at war, so we all are born as "children of wrath" (Eph 2:3) needing salvation from the wrath of God.
Because Adam's transgression we all are seperated from God and in need or reconciliation. We add to that transgression with our own, proving our rebellious, sinful nature.
God graciously sent His Son Jesus as a "second Adam" to take upon Himself the trasgressions of His people and avert the wrath of God through the cross.
1Cor 15:45
So also it is written, "The first MAN, Adam, BECAME A LIVING SOUL." The last Adam became a life-giving spirit.
By His death we are reconciled to God, though we were transgressors and sinners from our very conception.
Psa 51:5 Behold, I was brought forth in iniquity, And in sin my mother conceived me.
Rom 5:10 For if while we were enemies we were reconciled to God through the death of His Son, much more, having been reconciled, we shall be saved by His life.
As John Piper writes:
"If we don't understand "because all sinned" as "because all sinned in Adam," the entire comparison between Christ and Adam will be distorted and we won't see the greatness of justification by grace through faith for what it really is....
If Adam is the father of all human beings, and if the fundamental problem with all human beings is found in how we are related to Adam and what happened to us when Adam sinned, then everybody in the world, no matter when or where or whowhatever tribe or language or culture or ethnic identityeverybody has the same fundamental problem. And this means that if Jesus Christ is not just a Jew who died as a Jewish sacrifice for sins, but is also the "last Adam" or the "second man" (as Paul calls him in 1 Corinthians 15:45, 47), who provides a righteousness better than what we lost in Adam, then Jesus is no tribal God, or limited, local Savior. He is the one and only remedy for the divine judgment of condemnation that rests on every human soul. Which means he is a great Savior able to save persons from all times and all places and all peoples." - John Piper,
"Adam, Christ, and Justification"
http://www.desiringgod.org/library/sermons/00/062500.html
As to the question of Baptism, the Bible states:
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 is through the washing
regeneration, aka "baptism of the Spirit", which Baptism symbolizes and identifies us with, that we are freed from the bondage of sin that is ours through Adam's headship over us. We are "transferred from the kingdom of darkness" (in Adam) to the "kingdom of light" (in Christ) by that life giving Spirit, Jesus.
Some groups believe this occurs at baptism, but the Bible shows that regeneration (being born-again) occurs whenever the Spirit desires and is not based on the application of an outward sign. (Acts 10:44-47)