The invitation to be baptized for the first time, or be re-baptized regardless of whether you have had an LDS baptism or any other baptism, is renewed by Christ by revelation, and can be confirmed through prayer and individual revelation. In other words, the Lord Jesus Christ has sent forth the message that all are commanded (“command” means an invitation to “co”-operate with someone) to be baptized or re-baptized in his name in preparation for his return. This has nothing to do with any membership in an organization of men, and should not interfere with any obligations you have to any sect, party, or religion, but this baptism is just as much a requirement and part of the Gospel as any past Christian baptism you might have received, including LDS baptisms.
This sign is a witness that you keep Christ in your heart as a renewal of devotion to him before his Second Coming.
“And whoso believeth in me, and is baptized, the same shall be saved; and they are they who shall inherit the kingdom of God.
And whoso believeth not in me, and is not baptized, shall be damned” (3 Nephi 11:33-34).