The two bedrock passages concerning the theology of baptism are Romans 6:3-5 and Colossians 2:12.
In Rom 6:4 baptism not only symbolizes identification with Christ in his death, burial and resurrection; it declares our burial with him. It is precisely here that the true significance of the mode of baptism comes into play. Baptism is more than a bath, it is a burial, and only immersion can symbolize burial.
John Gill rightly said:
“. . . a corpse cannot be said to be buried when only a little earth or dust is sprinkled or poured on it.”
The focus of the New Testament authors is on baptism as immersion, and only rarely as baptism as an ablution. The reason for this, according to Ysebaert, is articulated by Paul in Romans 6:3,4 and Colossians 2:12, where the use of the Greek preposition eis in the final sense shows that Paul views immersion as being performed “with a view to Christ’s death, and for the purpose of the Christian’s participation in it.” The Christian’s descending into the tomb (buried with Christ) requires a corresponding act of ascending (rising with Christ).
If baptism has to do with death, burial and resurrection, does it not logically follow that immersion of a believer is an essential component of the rite of baptism? In fact, without immersion and without a believer, is there really any baptism in the New Testament sense of the term?
Even if it is argued that Romans 6:3, 4 has not a drop of water in it and is symbolic of spiritual baptism, we respond that the outward sign must correspond to the inner experience. Baptism commemorates the burial and resurrection of Christ, hence immersion. If it commemorates the believer’s death to sin and resurrection to new life, again immersion is the only mode that pictures this. If it symbolizes the washing away of sin, the symbol requires immersion since the thoroughness with which we are interpenetrated by sin calls for a washing that is potent enough to affect the whole body.
M. Pendleton was right on target: if baptism has to do with death, burial and resurrection,
“it follows inevitably that the immersion in water of a believer in Christ is essential to baptism–so essential that without it there is no baptism.” 
For Pendleton, sprinkling and pouring are as unlike a resurrection as they are a burial; immersion alone captures the symbol. Baptism is the instrument , note the Greek preposition dia, of burial. It is by means of baptism that burial is effected. Paul does not say we have been crucified with him by baptism” but “we have been buried with him by baptism.” It is not the manner of dying in view, but the finality of it.
Baptism symbolizes cleansing, but it is far more than a cleansing. To substitute sprinkling or pouring for immersion focuses on the cleansing only, but lacks the symbolism of the method of cleansing which is the cross of Christ. The tragedy of sprinkling or pouring leads, in the words of A. J. Gordon, to a
“bloodless moralism where the act of baptism is viewed as a kind of Christian circumcision, marking the sanctifying of human nature, and bringing it into covenant with God. How easily the idea of mystical efficacy becomes attached to the element of water, unless the form of its use be such as to carry the thought immediately and certainly to Christ crucified and dead.”
As Romans 6:3-5 makes clear, baptism is a symbol that we are risen with Christ spiritually (justification) and that we will rise bodily at the last day (glorification). We are clothed with righteousness now; we will be clothed with immortality then.
John Gill, A Complete Body of Doctrinal and Practical Divinity (Paris, Arkansas: The Baptist Standard Bearer, reprint of the 1839 edition), 911.
Ysebaert, Greek Baptismal Terminology, 50.
J. M. Pendleton, Distinctive Principles, 119.
A. J. Gordon, In Christ (New York: Fleming Revell, 1880), 74.