Confusion may arise from the fact that Paul says there is only one baptism (Eph. 4:5), but elsewhere the NT seems to refer to two types of baptism: one by water and another by the HS (Matt. 3:11, John 1:26-33, Acts 1:5). Any confusion is resolved by understanding that the two types of baptism are harmonized if baptism with water is viewed as a symbolic way of portraying baptism by the HS. (Most Bibles have a footnote for Mark 16:9-20 saying that the passage is not a reliable or well-attested part of the NT canon, so it is problematic to cite v.16 as requiring water baptism for salvation along with drinking poison or handling asps as signs of being saved.)
Both outward confession and water baptism may be seen as works manifesting love for God that every new Believer will want to (but we cannot say “must”) perform as soon as possible following his/her decision to have saving faith (cf. Matt. 3:13-15, Acts 2:38). Paul referred to the comparable moment for Abraham as spiritual circumcision. Although Paul did not command baptism, he administered it (in Acts 16:33, 18:8, 19:5 & 1Cor. 1:114-16) even though he said Christ did not send him to baptize but to preach the gospel (1Cor. 1:17). IOW, Paul’s focus was on preaching (spirit baptism) and he probably left the water baptizing to his assistants.
The outward evidence that someone was baptized by the HS and is Spirit-filled (Eph. 5:18) or walking with God is the manifestation of the fullness of Christ (Eph. 3:19, 4:13) or fruit of the Spirit, which consists of such attributes as those listed in Gal. 5:22-23: love, joy, peace, patience, kindness, goodness, faithfulness, gentleness and self-control. Jesus said “All men will know that you are my disciples if you love one another” (John 13:35, 1John 4:7-21), because “love” sums up the moral character of God (1John 4:7-8). He did NOT say “…if you are water baptized.”