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 – the Body of Christ; 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 and those who had “the faith of Abraham” before the Cross of Christ.
Baptism, first and foremost, is an act of God’s grace more than a human action. It is an outward and visible sign of an inward and spiritual/mystical truth. God has made water the way for humanity to be re-identified with Him. As such, the mode of baptism makes no difference. Whether sprinkled or dunked (and smothered, covered, or chunked; or I’ll hold you under until I get tired), 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 (enter into the water) and then we die with Christ (go under the water). Upon coming up out of the water it is Christ that is raised. We, our old fallen natures, are still buried under the watery death. It is no longer we who live, but Christ who lives in us – the Resurrection Life of Christ as our life for living.
“Why water?” you ask. “Water represents judgment,” I say. Water is the sign through which God destroys that which alienates us from His-self. It is through water baptism that creation is first identified with God in the Creation Deluge (Gen. 1:1-2). It is through water baptism that primitive humanity is re-identified with God in the Noahic Deluge. In the first, creation is baptized under Adam, being made from that which was created; signifying their identification with God. In the second, humanity is baptized under Noah, repopulated from his family; signifying their identification with God. Likewise, the Israelites were baptized through the Red Sea under Moses (1Cor. 10:2), signifying their identification with God (and not Pharaoh). And under the water baptism of Christ all humanity is identified, finally reconciling us to God, through His Baptism of Death (of which the previous water baptisms were precedents).
Thus, baptism is not so much a cleansing as it is a killing; a killing of our old nature of depravity – inherent from Adam, passing along through Noah (and Moses), and unified in the baptism of Christ and crucified on the Cross of Christ – and the Resurrection Life of our new nature in the Resurrected Christ; identified with Christ (as God’s exact image) and identifiable as the church (Christ’s express image), reconciling us to the original baptism of creation and its subsequent goodness in God (Gen. 1:4).