Admittedly, the word oikobaptism is an unusual and unfamiliar term. Yet, unlike other more familiar terms for baptism, oikobaptism captures more fully the essence of the apostles’ intent and purpose for baptism. Basically, it is a compound word made of the Greek words for household and baptism.
In his excellent essay The Oikos Formula, Jonathan M. Watt explains that “[t]he New Testament often uses family terminology in connection with baptism. This makes sense when we remember that a number of the metaphors describing conversion to Christ also involve family terms.” He observes rightly that Modern Christians (especially in the West) tend to regard household and family differently than ancient peoples did—whether Jews, Greco-Romans, or Christians—in the days of the apostles.
In the ancient Judeo-Christian context, from the beginning God established “the family as a social unit into which [he] put human beings and the channel through which he deals with them.” The family social unit included all who stemmed from or were connected to the head of the household. Likewise, in the Greco-Roman context the household included the master/husband/father and his wife and children, and “also the older generation (grandparents) and extended family, such as uncles, aunts, cousins, and various in-laws”  and perhaps even slaves.
In the ancient biblical-cultural worldview household meant more than nuclear family unit. It meant family-community. A household referred to a people, not just a place. As Watt explains, the Greek words for house (oikos/oikia) may be used to designate “either the residence (Acts 16:15b, 34) or the people who presumably live in it (Acts 16:15a; 18:8; 1 Cor. 1:16). So, when Luke reported that a person and his/her household were baptized he did not mean their domicile was baptized. He meant that their entire family-and-servants were baptized.
The practice of oikobaptism reported in the New Testament narrative is based on the principle of covenant households revealed in the Old Testament narrative. Households are one of the primary contexts in which the apostles and ministers of Jesus Christ administered the word and baptism to believing adults and their children (including infants). To outsiders this simply meant that everyone from the least to the greatest was baptized in solidarity with the head of the household. To insiders this meant that the whole household was initiated into a covenant relationship with God through Jesus Christ.
The English word for “baptism” is actually transliteration of the Greek word baptisma [-atos, -to]. In cultural usage the verb to baptizemeant (actively) to dip, immerse, or wash; or (passively) to be dipped, immersed, engulfed, or overwhelmed. The noun form of baptismrefers to washing and cleansing.
The word is found only in Christian writers because Jesus Christ and his apostles filled the word with theological meaning. Lexical definitions and etymological background studies are helpful, but they only tell a small part of the story of baptism. Neither actually explains what baptism is, much less what it signifies according to Christ and the apostles. Baptism is a theological concept which must, therefore, be defined according to the logic of the Word of God and explained in the light of the gospel.
For the apostles baptism was not defined by its physical mode of administration (e.g. affusion or immersion), rather it was defined by its deeper theological meaning (i.e., union with Christ and communion with the triune God and his covenant people).
Lexicons and dictionaries are good tools and they have a vital role to play in our studies. However, Christian theologians often do a better job of going beyond word studies to explaining the meaning and significance of baptism than the lexicographers. Their biblical and theological reflections allow them to tell the fuller story of baptism in context of real life. This is demonstrated clearly in the historic creeds, catechisms, and confessions of the Christian church.
Consider the following examples:
The Catechism of the Catholic Church defines baptism as
the basis of the whole Christian life, the gateway to life in the Spirit (vitae spiritualis ianua), and the door which gives access to the other sacraments. Through Baptism we are freed from sin and reborn as sons of God; we become members of Christ, are incorporated into the Church and made sharers in her mission: Baptism is the sacrament of regeneration through water in the word.
Martin Luther’s Small Catechism defines baptism as not simply common water, but it is water comprehended in God’s command, and connected with God’s Word…but with the Word of God it is a baptism—that is, a gracious water of life and a washing of regeneration in the Holy Ghost.
Similarly, the French Confession of Faith by John Calvin states that “baptism is given as a pledge of our adoption, for by it we are grafted into the body of Christ, so as to be washed and cleansed by his blood, and then renewed in purity of life by his Holy Spirit.”
The Westminster Confession of Faith describes baptism as
a sacrament of the New Testament, ordained by Jesus Christ, not only for the solemn admission of the party baptized into the visible Church; but also to be unto him a sign and seal of the covenant of grace, of his ingrafting into Christ, of regeneration, of remission of sins, and of his giving up unto God, through Jesus Christ, to walk in the newness of life. Which sacrament is, by Christ’s own appointment, to be continued in His Church until the end of the world.
Likewise, the Belgic Confession (Article 34) defines baptism as a sacrament
by which we are received into the Church of God, and separated from all other people as strange religions, that we may wholly belong to Him whose mark and ensign we bear; and which serves as a testimony to us that He will forever be our gracious God and Father.
Article XXVII of the Articles of Religion in the Anglican Book of Common Prayer states that
Baptism is not only a sign of profession, and mark of difference, whereby Christian men are discerned from others that be not christened, but it is also a sign of Regeneration or New-Birth, whereby, as by an instrument, they that receive Baptism rightly are grafted into the Church; the promises of the forgiveness of sin, and of our adoption to be the sons of God by the Holy Ghost, are visibly signed and sealed, Faith is confirmed, and Grace increased by virtue of prayer unto God.
Finally, the Baptistic Philadelphia Confession of Faith says
Baptism is an ordinance of the New Testament, ordained by Jesus Christ, to be unto the party baptized, a sign of his fellowship with him in his death and resurrection; of his being engrafted into him; of remission of sins; and of his giving up into God, through Jesus Christ, to live and walk in newness of life.
There are several points of agreement between these definitions and descriptions of baptism. All agree that baptism was instituted by the Lord Jesus Christ. All agree that it is a water-rite of initiation which introduces baptized persons to Christ and his church. All the traditions represented here — with only one exception — agree that baptism is rightly administered to believers and their children – including infants – with water and the word. The point here is that some form of oikobaptism is the majority position.
All Christians know what baptism is when they see it, yet there is more to it than meets the eye. Despite all the lexical definitions and theological descriptions, baptism defies exhaustive definition and remains a mystery. The “unknown” invites the contemplative Christian to dive deeper into the mystery of gospel of Christ. That calls for more than lexical word studies or ecclesiastical descriptions. It calls for prayer and exegetical reflection on the Holy Scriptures.
To state the obvious, baptism was instituted by the Lord Jesus Christ when he sent his apostles to make disciples of all the nations by baptizing them in the one name of the Holy Trinity and by teaching them to obey all his teachings on the basis of his authority (Mat 28:18-19). Commenting on that text, N. T. Wright explains that baptism is “the public, physical and visible way in which someone is marked out, branded almost, with the holy ‘name’. The ‘name’ which we are all to share is the new name of the living God – the Father, the Son, and the Holy Spirit.” Likewise, Dr. Sinclair Ferguson describes baptism as a special naming ceremony:
In baptism, the name of the Lord is given to us (Mat 28:18-20). Baptism is a naming ceremony. In this sense baptism into the name of the Father, Son, and Holy Spirit consummates the triune covenant blessing of the Mosaic epoch (Num 6:22-27).
Pastor-theologian Peter Leithart explains that “receiving the name of the Triune God in baptism means that we are made part of a new family, the church, and that we are to present ourselves to the world bearing this name well.” Baptism is a status-changer. It is the means by which a person becomes a bearer of the sacred name of God and a member of God’s covenant people.
In sum, by the authority of the Lord Jesus Christ the covenant sign of baptism is to be applied to his people, yet it is administered with a set of covenant stipulations. God places his sacred name on all the baptized members of a household, and he requires all baptized persons to live by his household code and obey all the teachings of the Lord Jesus Christ.
Next: Biblical Foundations
 Strawbridge, Gregg, ed. The Case for Covenantal Infant Baptism. P & R Publishing, 2003. p 72
 Ryken, Leland. Dictionary of Biblical Imagery. Downers Grove Ill.: InterVarsity Press, 1998. p 265
 Strawbridge, p 79
 Ibid, p. 77
 BAGD, p 132
 The discussion about the proper mode(s) of baptism is important for purposes of application and administration, however it falls outside the parameters of the present study. Suffice it to say that a strong biblical case can be made for sprinkling, pouring, and immersing as proper modes of baptism. See Calvin’s Institutes: “Whether the person baptised is to be wholly immersed, and that whether once or thrice, or whether he is only to be sprinkled with water, is not of the least consequence: churches should be at liberty to adopt either, according to the diversity of climates, although it is evident that the term baptise means to immerse, and that this was the form used by the primitive Church. (4:15:19)”
 Nettles, Tom J, Richard L Pratt, and Robert Kolb. Understanding Four Views on Baptism. Grand Rapids, Mich.: Zondervan, 2007. p 176
 Ibid, p 177
 The Westminster Confession of Faith and Catechisms, Chapter XXVIII, Of Baptism 1., Lawrenceville Ga.: Christian Education & Publications Committee of the Presbyterian Church in America, 2007
 Book of Common Prayer (1929)
 Wright, N. T. 2002. Matthew for everyone. Part 2. London: SPCK.
 Wright, David F., Sinclair B. Ferguson, A. N. S. Lane, and Bruce A. Ware. 2009. Baptism: three views. Downers Grove, Ill: IVP Academic., pp. 89-90