One of the more perplexing problems a congregation faces is what to do about people who were baptized into a denomination and later learned the truth. Do they need to be baptized again? If so, what about Ephesians 4:4?
Most denominations baptize for reasons that are incorrect. A majority of denominations baptize, sprinkle, or pour as an outward sign to the world that someone has been saved. The scriptures teach that believers were baptized to wash away sins (1 Peter 3:20-21; Acts 2:38). In the book of Acts, only those who were believers were baptized. This baptism took place before the point of salvation.
Ephesians 4:4 does indeed teach that there is one baptism, but denominations have created many different reasons for baptism. Therefore, if you were baptized in a denomination that practices a baptism not found in the scriptures, you have not followed the instruction in Ephesians 4:4 and need to be baptized again. The one true baptism is the one found and explained in the Bible.