Valid Baptism has a permanent effect on the soul, it embeds on it a seal, a hallmark, that never goes away, no matter what happens.
The one who has been baptized with water, with the words:
"I baptize you in the Name of The Father, and of The Son and of The Holy Spirit" becomes a Child of God.
Some might argue that we are all children of God, and it is true that we are all His creatures; God created all of us in the order of nature, through our parents,
but Baptism gives us God's supernatural stamp,
we become sons and daughters of God, brothers and sisters of Jesus. The love and fidelity to God Our Father, shown to us by Jesus, is implanted in us.
Baptism is necessary to enter the Kingdom of Heaven.
The Sacrament of Baptism imparts on the baptized God's sanctifying grace; Divine Life.
The 3 Persons of The Holy Trinity is grafted into the soul; this imprint grants supernatural strength and power which makes us children of God.
It washes away sins; for infants we are talking about original sin, but in the case of adult baptism it also washes away all actual sins committed.
The baptized becomes member of the Church, it is the entrance into the community of the universal Church, and all the other Sacraments of the Church depends on this first one.
Baptism is a new birth, a regeneration; the person has been born into the world by natural birth parents, now the baptized is being born again, in the supernatural order, so it needs another set of parents; God parents.
The washing with running water which flows, in the same way as we wash ourselves, is because the ritual corresponds to the natural reality of washing our bodies, as we know it.
Baptism is the visible sign that signifies what it produces and produces what it signifies.
Baptism is also a public proclamation of faith in Jesus Christ.
