Mark 1:4 New English Translation

⁴In the wilderness^[a] John the baptizer^[b] began preaching a baptism of repentance for the forgiveness of sins.^[c]

Mark 1:4 tn Or “desert.”
Mark 1:4 tn While Matthew and Luke consistently use the noun βαπτίστης (baptistēs, “[the] Baptist”) to refer to John, as a kind of a title, Mark prefers the substantival participle ὁ βαπτίζων (ho baptizōn, “the one who baptizes, the baptizer”) to describe him (only twice does he use the noun [Mark 6:25; 8:28]).
Mark 1:4 sn A baptism of repentance for the forgiveness of sins was a call for preparation for the arrival of the Lord’s salvation. To participate in this baptism was a recognition of the need for God’s forgiveness with a sense that one needed to live differently as a response to it.

New English Translation (NET)