John’s baptism was and remained a “baptism of repentance”…those who were baptized by him were not yet Christians…did not receive the Sacrament.
In Acts those when those who had been baptized only by John were encountered…they had to be baptized with Christian baptism…and then received the Holy Spirit…
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The Catechism of the Catholic Church:**
720 Finally, with John the Baptist, the Holy Spirit begins the restoration to man of “the divine likeness,” prefiguring what he would achieve with and in Christ. John’s baptism was for repentance; baptism in water and the Spirit will be a new birth.
Johns Baptism was for repentance…it is only with Christian Baptism that one will be baptized in water and the Spirit …and it is the baptism that brings new birth.
"Returning now to the Gospel passage, let us seek to better understand what is happening today. St Mark recounts that it was just when John the Baptist was preaching on the banks of the River Jordan, proclaiming the urgent need for conversion in view of the now imminent coming of the Messiah, that Jesus, who was among the crowds, presented himself to be baptized. John’s Baptism is
indisputably a Baptism of penance,
very different from the sacrament that Jesus was to institute. "–
Pope Benedict XVI
vatican.va/holy_father/benedict_xvi/homilies/2009/documents/hf_ben-xvi_hom_20090111_battesimo_en.html
The baptism John offers is one of repentance, a sign that is an invitation to conversion, to a change of life, because One is coming who will “baptize with the Holy Spirit and with fire” (3: 16). —
Pope Benedict XVI
vatican.va/holy_father/benedict_xvi/homilies/2010/documents/hf_ben-xvi_hom_20100110_battesimo_en.html