Definition and Origin:
Baptism is a Christian sacrament and ordinance that signifies the believer's faith in Jesus Christ and their identification with His death, burial, and resurrection. The term "baptism" is derived from the Greek word "baptizo," meaning "to immerse" or "to dip." This practice finds its roots in the New Testament and is a central rite in Christian tradition.

Biblical Foundation:
Baptism is prominently featured in the New Testament, beginning with the ministry of John the Baptist, who called people to repentance and baptized them in the Jordan River. In Matthew 3:11, John states, "I baptize you with water for repentance, but after me will come One more powerful than I, whose sandals I am not worthy to carry. He will baptize you with the Holy Spirit and fire."

Jesus Himself was baptized by John, marking the beginning of His public ministry. Matthew 3:16-17 records, "As soon as Jesus was baptized, He went up out of the water. Suddenly the heavens were opened, and He saw the Spirit of God descending like a dove and resting on Him. And a voice from heaven said, 'This is My beloved Son, in whom I am well pleased.'"

Theological Significance:
Baptism is a public declaration of faith and a symbolic act of obedience. It represents the believer's cleansing from sin, as well as their union with Christ in His death and resurrection. Romans 6:3-4 explains, "Or aren’t you aware that all of us who were baptized into Christ Jesus were baptized into His death? We were therefore buried with Him through baptism into death, in order that, just as Christ was raised from the dead through the glory of the Father, we too may walk in newness of life."

Mode and Practice:
The mode of baptism varies among Christian denominations, with immersion, pouring, and sprinkling being the most common methods. The early church practiced baptism by immersion, as suggested by the account of Philip and the Ethiopian eunuch in Acts 8:38-39: "And he gave orders to stop the chariot. Then both Philip and the eunuch went down into the water, and Philip baptized him. When they came up out of the water, the Spirit of the Lord suddenly took Philip away, and the eunuch did not see him again, but went on his way rejoicing."

Infant vs. Believer's Baptism:
The practice of infant baptism is observed in some Christian traditions, based on the belief that baptism is a means of grace and a sign of the covenant, akin to circumcision in the Old Testament. However, other denominations advocate for believer's baptism, emphasizing personal faith and repentance as prerequisites. Acts 2:38 supports this view: "Peter replied, 'Repent and be baptized, every one of you, in the name of Jesus Christ for the forgiveness of your sins. And you will receive the gift of the Holy Spirit.'"

Great Commission:
Baptism is integral to the Great Commission, where Jesus commands His disciples to make disciples of all nations. In Matthew 28:19-20, He instructs, "Therefore go and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, and teaching them to obey all that I have commanded you. And surely I am with you always, to the very end of the age."

Conclusion:
Baptism remains a vital expression of faith and obedience in the Christian life, symbolizing the believer's new identity in Christ and their commitment to follow Him.