“Or do you not know that all of us who have been baptized into Christ Jesus have baptized into His death” (Romans 6:3)?
Paul’s normal use of “do you not know” is in regard to those things with which his audience is already familiar. Here, however, he is educating them on something they had not yet considered. Just as he wrote of the children of Israel being baptized into Moses (1 Cor.10:2), and believers being baptized into one body (1 Cor.12:13), Paul continues the same figurative and metaphorical use of the term baptism to describe believers being immersed into Christ and his death. Thus, emphasizing that as the Messiah, the representative of the people, what is true of him is true of all who believe and trust in him.