In the first century the coming of the King and the Kingdom was at hand. John the Baptist was sent out to prepare the people for the coming of the King:
"In those days came John the Baptist, preaching in the wilderness of Judaea, And saying, Repent ye: for the kingdom of heaven is at hand. For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight" (Mt.3:1-3).
It was necessary for the people to have a change of mind in regard to their sinful life style in order "make ready a people prepared for the Lord" so that they
"might serve Him...in holiness and righteousness" (Lk.1:17,74-75).
Those who submitted to the rite of water baptism were acknowledging their sinful lifestyle and pledging to change their way of life in order that they might serve the Lord. In exchange, they were given the knowledge that their past sins were forgiven and that they were beginning their service for the Lord with a clean slate.
However, since the people rejected their promised King His return to set up His Kingdom has been postponed and it will not be until He returns to the earth when the Kingdom will be at hand:
"And then shall they see the Son of man coming in a cloud with power and great glory. And when these things begin to come to pass, then look up, and lift up your heads; for your redemption draweth nigh. And he spake to them a parable; Behold the fig tree, and all the trees; When they now shoot forth, ye see and know of your own selves that summer is now nigh at hand. So likewise ye, when ye see these things come to pass, know ye that the kingdom of God is nigh at hand" (Lk.21:27-31).
At the present time we are not waiting for the Lord Jesus to return to the earth. Before that can possibly happen certain events must first take place, such as the setting up of the abomination of desolation in the holy place (Mt.24:15). Therefore, the purpose of water baptism, to prepare a people for the return of the Lord Jesus, is no longer in order.