[b]John the Baptist appeared in the wilderness preaching a baptism of repentance for the forgiveness of sins [that is, requiring a change of one’s old way of thinking, turning away from sin and seeking God and His righteousness]. And all the country of Judea and all the people of Jerusalem were continually going out to him; and they were being baptized by him in the Jordan River, as they confessed their sins. John wore clothing made of camel’s hair and had a [wide] leather[c]band around his waist, and he ate locusts and wild honey. And he was preaching, saying, “After me comes He who is mightier [more powerful, more noble] than I, and I am not worthy to stoop down and untie the straps of His sandals [even as His slave]. As for me, I baptized you [who came to me] with water [only]; but He will baptize you [who truly repent] [d]with the Holy Spirit.” – Mark 1:4-8
When a person becomes a believer they receive the Holy Spirit. However, when a believer is filled with the Spirit—the Holy Spirit gets more of them.
One of Christ’s key missions was to baptize His people in the Holy Spirit. He instructed His disciples not to begin witnessing until they were baptized in the Holy Spirit and endued with power. Jesus Christ Himself did not enter His ministry until He had been ‘anointed . . . with the Holy Ghost and with power’.
Repent was the first word of Jesus’ gospel. Faith in Christ is essential for baptism.
The baptism of the Holy Spirit is something that the early church was so accustomed to, that it was fit to tell everybody to pray in the Holy Ghost. When the early church found believers who hadn’t yet received the gift of the Holy Ghost, they made it a priority to get them baptized in the Holy Ghost.