D&C 22 – 23
To accept the baptisms of other churches is to imply that there is no difference of authority and that different paths can all lead to Christ. There is only one path, and one authority, thus there can be only one baptism. Those how have not received that baptism must be baptized if they are to receive the covenant.
I love the subtle differences in the counsel to each of the 5 brethren addressed in section 23. Samuel was not yet called to preach before the world. Joseph Knight was to take up his cross before the world Oliver was to make his calling known to the world and the church. Hyrum and Joseph Smith Sr. were called for the rest of their lives to exhort and strengthen the church.