[A little context. I'm a former baptist attending a PCA church and still on the fence regarding paedo/credo, but leaning credo.] My understanding is that the large majority of baptist churches as well as the 1689 Confession require baptism by immersion and would require an individual to be baptized by immersion as a believer for church membership and especially to hold office. There seem to be a minority of churches with somewhat more relaxed policies. I agree that there is a reasonable scriptural and historical case for baptism by immersion - I'm not asking about that specifically. However, I would not say that the case is airtight. There are no clear instructions for how baptism is specifically carried out in the scripture. I do believe that someone could honestly conclude from the scriptures alone that (say) sprinkling is an acceptable mode. What I'm curious to better understand is why most baptists believe that a water baptism by sprinkling/pouring is sufficiently invalid that an individual with such a baptism must be rebaptized by immersion.