We are saved only by grace through faith (Eph. 2:8-9). We cannot be saved by practicing religion, good works and behavior, ceremony, or even personal sacrifice; only God's grace is sufficient, and is extended to all humanity (Acts 10:34-35). Our faith justifies us in the sight of God (Rom. 1:16-17, 5:1). We are to express our faith by calling on him (Rom. 10:9-10, 13) and obeying the plan of salvation(Acts 2:38). This is not optional; faith alone will not save, unless it is accompanied by action (Jam. 2:20, 22, 24, 26).
Repentance involves several things: a recognition of and sorrow for one's sins (2 Cor. 7:10-11); a recognition of the judgment upon sin; and an acceptance of God's grace. It brings a hatred of and determination to forsake sin. This is not to say that a Christian will never sin again; but if we confess our sins, God will cleanse us of them (I John 1:8-9), though we should not willfully continue in sin (Rom. 6:1-2, 6-7).
Water baptism is the method by which our sins are washed away by the blood of Jesus; it is symbolic of the burial of Christ. Jesus taught that salvation was impossible without it (John 3:5) and commanded his disciples to baptize those they taught (Matt. 28:19). There is only one baptism (Eph. 4:4-6): submersion in the name of Jesus Christ, the only name with saving power (Acts 4:10, 12).
The baptism of the Holy Ghost is an experience unique to the New Testament Church, though the Old Testament prophets and John the Baptist spoke of its coming (Joel 2:28-29; Isa. 28:11-12; John 1:33-34; Matt. 3:11; Luke3:16). Jesus foretold the availability and necessity of the Holy Ghost (John3:3, 5), but said that the gift would not be given until after his ascension (John 7:37-39; 16:7). The Holy Ghost was first poured out on the first Day of Pentecost following Jesus' death (Acts 2:1-4).
The Holy Ghost is the ultimate fulfillment of our salvation. It makes us part of the body of Christ (I Cor. 12:13) and grants access to God(Eph. 1:13-14;2:18). It sanctifies (Rom. 15:16; I Cor. 6:11), and serves as a witness to the world that we are God's children (Gal. 4:5-6; Rom. 8:15-16).
The reception of the Holy Ghost is evidenced by the speaking of "other tongues," or a language unknown to the speaker. On the Day of Pentecost, all of them were Jewish, yet they were heard speaking in a multitude of languages. Throughout the book of Acts, this is how Christians recognize that others have recieved the Holy Ghost (Acts 10:44-46; 11:15-18; 19:6).