Baptism
Since people typically wash using water, baptism is often seen as symbolic of having our sins washed away. That is true, but here, Paul uses different symbolism. He says baptism is like dying with Jesus when the person goes under the water and being resurrected with Him when the person comes out. He says our lives should reflect this change; we should no longer live the way we used to before trusting Jesus. If a person trusted Jesus to take care of their sin, why would they want to continue in that sin?
Are you living like Jesus by having been baptized and also living like a new person? Have you embraced that the old you is dead?