The concept of baptism had its origin as a washing in, with, or by water, suggesting the ceremonial cleansing of a person.  Its spiritual significance can be seen first in the Old Testament, as when the Law required the bathing of persons who were considered ‘unclean’ (Leviticus 14:8-9; see also Leviticus 15).  On the Day of Atonement, Aaron the priest was to bathe himself both before and after entering the holy place (Leviticus 16:3-4).  Even from the beginning of their priestly ministry, Aaron and his sons were ceremonially washed at their initial ordination for ministry (Leviticus 8:5-6).  However, not all of these ‘baptisms’ were immersions of people into water.  Many of the instances of washings mentioned in the Old Testament were simply the cleansing of the hands as a symbolic gesture of holiness before God.  The obvious symbolism conveys the need for the cleansing of the heart in repentance and for the sake of spiritual service (Psalm 51:1-2, 7-10).
Baptism took on a different significance with the baptism of John.  (This era, including John’s baptism and ministry, has been commonly called, ‘Pre-Christian Judaism.’) Although this era called for the full immersion of a Gentile into water-which signified their complete initiation into Judaism, (commonly called, ‘Jewish proselyte-baptism’)-baptism in pre-Christian Judaism signified an inward repentance and faith.  No one knows whether Jewish proselyte-baptism influenced the pre-Christian era regarding baptism like that of John the Baptist, but the two have striking similarities.  John the Baptist preached a ‘baptism of repentance for the forgiveness of sins’ (Mark 1:4), a parallel to the Gentiles proclaiming their complete allegiance to Judaism (which along with baptism, would also include a Gentile becoming circumcised and his offering up animal sacrifices to God).  This is precisely why John the Baptist reacted angrily to the Pharisees and Sadducees, who were coming to him for baptism. Matthew 3:7-8 records that ‘when he saw many of the Pharisees and Sadducees coming for baptism, he said to them, ‘You brood of vipers, who warned you to flee from the wrath to come? Therefore bear fruit in keeping with repentance’.’ Since they would have already understood Jewish ceremonial washings, they came to John for his baptism.  However, they did not possess the requisite repentance in order for John’s baptism by immersion to take place (see John 3:22-25).  Thus, the baptism of John laid the foundation for the proper understanding of the later, ‘Christian baptism.’ This ‘Christian baptism’ was instituted by Christ Himself when He commissioned His disciples to ‘go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you; and lo, I am with you always, even to the end of the age’ (Matthew 28:19-20).
Regarding the proper understanding of the ordinance of water baptism, the word ‘baptism’ itself is a transliterated English word which originates from the two Greek verbs, bapto (bap’-to) which means, ‘to dip into,’ like dipping a cloth into dye; or baptizo (bap-tid’-zo), which means, ‘to fully dip into’ or ‘to immerse.’ Controversy among various baptismal modes notwithstanding, individuals are not sprinkled, but literally immersed into water (Matthew 3:6,13,16; Mark 1:5,9-10; John 1:26, 3:23; Acts 8:36-38).  This literal immersion into water becomes a powerful metaphor for the believer’s death to self and resurrection to a new life in Christ.  Indeed, the apostolic teaching on baptism primarily signifies the believer’s union with Christ.  If Christian baptism is to be properly understood, it should be defined as the complete immersion of a believer into water, which as the apostle Paul says, spiritually symbolizes his death to sin, and his burial and rising again in order to walk in newness of life (Romans 6:3-4; cf.  also Colossians 2:12).  Colossians 3:9-14 and Ephesians 4:22-24 both speak of the imagery of the believer putting off the clothes of the ‘old life,’ and likewise putting on the clothes of the ‘new life.’ This could well signify the baptismal ceremony of the early church, where the believer would remove his old garments of the common life, and put on his baptismal robe of the new, resurrected life.  Paul told the Galatians: ‘All of you who were baptized into Christ have clothed yourselves with Christ’ (Galatians 3:27).  The spiritual significance of baptism is lost if the concept of immersion is dismissed.
Practically speaking, the command for the believer to be baptized is a time for the declaration of his faith in Christ.  The Bible teaches that once a person had come to Christ in repentance and faith, he was subsequently baptized.  By looking at the pattern of the early church, those who were converted to Christ were then baptized (see Acts 2:38,41; 8:12-13; 8:36-38; 9:17-18; 16:31-33).  One can easily see from these passages that baptism was a believer’s act of obedience, which would signify the new condition of the heart.  It has been stated by some, however, that baptism and conversion were so linked in the early church that they had become synonymous (some believe Acts 2:38 explicitly teaches this).  But since we know that regeneration comes before baptism (see especially Acts 8:36-38; 16:31-33), baptism can never be a condition or a requirement for salvation (see 1 Peter 3:21-22).  The apostle Peter himself clarified that water baptism does not save-that literal immersion into water is not efficacious.  It is simply the outward expression of the conscience being renewed through Christ’s work of redemption and resurrection.  The fact that water baptism is not required for salvation is evidenced by the promised gift of eternal life by Christ to the thief on the cross.  Although the thief was unable to participate in baptism prior to his death, Christ nevertheless declared to him that he would-that very day-be with Christ in paradise (a reference to heaven).  The entire picture of the thief’s inability to undergo baptism proves that baptism cannot be a necessary work for salvation.  Scripture declares in unmistakable language (Ephesians 2:8-9; Romans 3:20-28; Titus 3:5-7) that man is not saved by works of any kind, his salvation being based solely upon the merits of Christ’s work on the cross, which is then credited to the sinner’s account.  Since justification occurs prior to water baptism, it cannot then be a condition for salvation.  Therefore, let each person who has truly repented of his sin, only then become water baptized for the public proclamation of his faith in the name of the Father, and the Son, and the Holy Spirit.