How shall we approach the doctrine of baptism? Can we simply search through the concordance for every occurrence of the word, carefully exegete each passage in context and then come to conclusions about the meaning of baptism? Superficial consideration may suggest that this basic approach is not only legitimate, but the only possible method. How else can we discover the meaning of a Biblical word? This is the approach generally taken by Baptists, most of whom insist that any other approach distorts the meaning of baptism in order to force it to fit alien theological contexts. William Shirreff, whose lectures on baptism come recommended by Charles H. Spurgeon, insists at great length that "the Scriptures of the New Testament are the only rule to direct us in regard to the positive institutions of the Gospel." 
It is my contention in this paper that there are Biblical reasons for rejecting this approach. In a sense, however, my rejection of this approach is partially based upon this approach. In other words, when we examine the New Testament passages about baptism we discover that baptism is part of a larger theological idea--the Biblical doctrine of the covenant. It is the covenant that supplies the answer to the most basic questions of water baptism: Why should Christians practice baptism? What does baptism mean? Who is qualified to receive baptism? No matter what our understanding of baptism is, we are forced to consult some larger theological context. We cannot avoid the question: How does baptism fit into the whole context of the Biblical teaching about man's relationship to God. Also, any approach must consider the larger context of Biblical ceremonial teaching in general as an aspect of man's relationship to God.
But it should not be thought that we impose these theological considerations on the text of the Bible. It is rather the Bible, specifically the New Testament, that forces us to think in broader theological terms. There are at least three types of passages that compel us to examine the Old Testament to understand the doctrine of baptism.
First, there is the ministry of John the Baptizer. John is a transitional figure, a prophet of the old covenant preparing the way for the new. Jesus specifically identifies John as a prophet of the old covenant:
"Verily I say unto you, Among them that are born of women there hath not risen a greater than John the Baptist: notwithstanding he that is least in the kingdom of heaven is greater than he. And from the days of John the Baptist until now the kingdom of heaven suffereth violence, and the violent take it by force. For all the prophets and the law prophesied until John. And if ye will receive it, this is Elias, which was for to come" (Mat. 11:11-14; cf. Mat. 17:11-13; cf. Luk. 3:3ff.).
John was not merely an Old Testament prophet, he was a prophet, like Ezekiel, from a priestly family (Luk. 1:5). John's baptism, thus, was an old covenant ceremony conducted by an old covenant priest. In this connection it is important to note that when he was examined by the priests and levites, they made no objection to the practice of baptism; they only questioned his authority to baptize (John 1:19ff.), suggesting that John's baptism conformed to Jewish ceremonial standards.
Everything that the New Testament tells us about John, in other words, points us to the old covenant and its ceremonies as the only possible source of understanding. How would an old covenant prophet, especially one belonging to a priestly family, practice "baptism"? What does "baptism" mean to priests and levites in the days of Jesus? Can anyone answer these questions honestly or Biblically without considering the Old Testament?
A second type of New Testament passage that compels us to consider the Old Testament background of baptism is those passages that refer to old covenant ceremonial washings as "baptisms." Mark refers, for example to the pharisees' perversion of the Old Testament system of ceremonial washings as "baptisms" (Mark 7:1-8). The book of Hebrews identifies the old covenant ceremonial washings themselves as "baptisms" (Heb. 9:10). The word "baptism," then, is clearly not a technical term that only refers to Christian baptism. The New Testament tells us that the Old Testament ceremonial washings are also baptisms.
A similar type of passage, although not speaking of regular Old Testament ceremonies, is seen in Paul's epistle to the Corinthian Church, which had experienced various problems with baptism (1 Cor. 1:11-17). Paul, in a context emphasizing the relevance of the Old Testament for Christians, says that Israel fleeing from Pharaoh's army was "baptized unto Moses in the cloud and in the sea" (1 Cor. 10:2). Taking into consideration both the facts that the Corinthian Church had problems with baptism and that Paul's purpose here is to stress the importance of the Old Testament teaching, this passage is especially meaningful.
The third, and most significant type of passage is found in the New Testament teaching about baptism and the Lord's Supper. Both of the Christian ceremonies are clearly depicted as covenantal ceremonies. Baptism in particular is expressly designated as a covenant ceremony like circumcision in the Old Testament (Col. 2:11-12). The Lord's Supper is called the new covenant in His blood (1 Cor. 11:25) and is also said to be analogous to the passover (Luk. 22:15ff.; 1 Cor. 5:7ff.).
When the New Testament itself places the doctrine of baptism and the related doctrine of the Lord's Supper in the larger context of the covenant, we are obligated to consider the whole teaching of the Bible on the subject of the covenant and the whole idea of covenantal ceremonies. To entirely separate the new and old covenants is virtually to posit two different religions in the Bible, one for people before the coming of Christ and another for those after His coming. This is certainly not the teaching of the Bible. Paul, for example, argues in various epistles that the Christian religion is the fulfillment of the religion of the old covenant, that we are saved just as Abraham was saved, that Christians are the true heirs of the Abrahamic covenant, that to keep the true teaching of the law and the prophets is to believe in Jesus. Neither Paul or any other New Testament writer even suggests that the new covenant is different from the old covenant in its fundamental principles. Paul believed he was continuing the teaching of the law and the prophets at the higher level of new covenant fulfillment, not that he was replacing a dead religion with a living one.
To restate this point in different terms, to argue that the doctrine of baptism is part of the larger Biblical teaching on the covenant is simply to argue that the Bible is one book, not two. Indeed, the very idea of dividing the Bible into two books, the Old Testament and New Testament, while convenient for purpose of reference, like chapter and verse divisions, is not a Biblical idea. The Bible is one book from Genesis to Revelation. It is not two books under one cover, the older part of which is believed by Jews and the newer part of which is believed by Christians.
The so-called Old Testament is an incomplete revelation which Jesus came to complete. The Gospels, Acts, the epistles and the Revelation of John complete the revelatory project that began with Moses. We must insist that the Bible is one, its religion is one, its teaching is unified and that everything taught in the Bible, although not directly addressed to us and perhaps not directly applicable, is applicable in some manner: "All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works" (2 Tim. 3:16-17).
Examination of the New Testament references to baptism informs us in no uncertain terms that no "declaration of independence" can separate the doctrine of baptism from old covenant ceremonies or the doctrine of the covenant. The example of John the Baptizer, the explicit use of the word baptism to refer to old testament ceremonies, and the express identification of both baptism and the Lord's Supper as covenantal ceremonies compel us to construct a "whole-Bible" doctrine of baptism as opposed to a merely "New Testament" doctrine of baptism.
If we read the Bible beginning from Genesis rather than Matthew, a covenantal meaning for baptism and the Lord's Supper is what we expect since all religious ceremonies in the Old Testament are covenant making or covenant renewal ceremonies. Ceremonies in the Bible are not magical, as in paganism, nor are they mere ceremonies, outward rites practiced merely for their educational value.
Given the covenantal nature of Biblical religion, how could the new covenant ceremonies of baptism and the Lord's Supper be fundamentally different from the old covenant ceremonies which they replace? And how is it possible for us to have a Biblical understanding of new covenant ceremonies unless we study them in the light of the old covenant ceremonies which they fulfill?
 William Shirreff, Lectures on Baptism (London: Passmore and Alabaster, 1878; reprinted by: Ft. Smith, Arkansas: The Baptist Standard Bearer, 1987), pp. 12-33.