John's baptism

Luke 3:3
And he came into all the country about Jordan, preaching the baptism of repentance for the remission of sins;

Wait, what? Didn't Paul say there is only one baptism (Eph 4:5)? And that baptism was into Christ's death? Why is John's baptism valid when Christ has yet to die on the cross?
Paul mentioned about the baptism of John in Act 19:4 and part of the point being to direct people to Christ. Was it useful for Salvation? Yes, while it lasted! The same concept applies to people in the OT era. At whatever dispensation, obedience to God is key. Christ being foreordained before the foundation of the world (1Pe 1:20; Rev 13:8) to save the world, “paid it forward and back” for all.
That’s why it was necessary for the Ephesians in Act 19 to be “re-baptized”, and that second time into Christ, because they were amenable to the New Testament law, then being made in place upon the death of Christ (Heb 9:16,17)
And just as we are not governed by OT law, neither does John's baptism apply today as well.