That's because in Jewish ritual baptisms one was baptized by the authority of the given teacher they were following ... Some sectarians were now claiming to be disciples of Paul ... Apollos and Cephas ... Paul was simply reminding them under whose authority and power they had been baptized under.
In baptism we publicly declare to be His disciples.
Exactly! I believe that's why so much emphasis was given about "the name".
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Master of Science in Applied Disgruntled Religious Theorist Wrangling
PhD in Petulant Tantrum Quelling
Dean of the School of Hard Knocks