While baptism is the means by which one enters the membership role of his/her local church, it is in actuality entrance into the identifiable “Catholic” (i.e. Universal) Church; which is both, visible and invisible, and earthly and at the same time heavenly. So, yes, baptism is technically a joining of the church, though not simply the local but the Universal (which traces itself back to the original disciples, but also those who had “the faith of Abraham” before the Cross of Christ).
Furthermore, besides baptism making one identifiable in the Catholic Church, it is also about identity. Baptism, first and foremost, is an act of God’s grace more than an act of human will. As such, the mode of baptism makes no difference. Whether sprinkled or dunked – smothered, covered, or chunked – Baptism is about God and our identity in His Son, not by what means we are baptized. However, the act of submersion is a better analogy of God’s grace at work.
In the sign of baptism, we are first buried with Christ and then we die with Christ. Upon coming up out of the water it is Christ that is raised. We, our old fallen natures, are still buried under the waters of death. It is no longer we who live, but Christ who lives in us – the resurrection of Christ in us. You ask, “Why water?” I answer, “Because water represents judgment.”It is through water that God first redeemed creation (Gen. 1:1-2). It is through water that God redeemed primitive humanity in the Noahtic Deluge (“Noah’s Flood”). In the first flood humanity is baptized under Adam (being made from that which was created) signifying their identity in him. In the Noahtic flood humanity is baptized under Noah, signifying their identity in him. Likewise, under Moses the Israelites were baptized through the Red Sea signifying their identity in Moses (1Cor. 10:2). And under Christ all humanity (Jew or non-Jew), is once again identified with God in Christ.
Thus, our baptism is a killing of our old nature – inherent from Adam, passing along through Noah (and Moses), and crucified with Christ on His cross – and the resurrection of our new nature is identified in Christ (as God’s exact image) and identifiable as the church (Christ’s express image); returning us to the original baptism of creation and its goodness (Gen. 1:4).
Baptism is so much more than membership into a local church. The Baptism of Death signifies a killing of the old fallen nature and a resurrection of the new creation in Christ (Mark 10:38-39).
