Adam Clarke on Romans 6:3

Know ye not, etc. - Every man who believes the Christian religion, and receives baptism as the proof that he believes it, and has taken up the profession of it, is bound thereby to a life of righteousness. To be baptized into Christ, is to receive the doctrine of Christ crucified, and to receive baptism as a proof of the genuineness of that faith, and the obligation to live according to its precepts.

Baptized into his death? - That, as Jesus Christ in his crucifixion died completely, so that no spark of the natural or animal life remained in his body, so those who profess his religion should be so completely separated and saved from sin, that they have no more connection with it, nor any more influence from it, than a dead man has with or from his departed spirit.