Yesterday, I attended the baptism of a friend.
During the talk on baptism, the speaker quoted Mosiah 18:9
Yea, and are willing to mourn with those that mourn; yea, and comfort those that stand in need of comfort, and to stand as witnesses of God at all times and in all things, and in all places that ye may be in, even until death, that ye may be redeemed of God, and be numbered with those of the first resurrection, that ye may have eternal life—
She used it to indicate that one of the things we covenant to do when we are baptized is to mourn and comfort those who need it. Except, we don’t actually make that covenant at baptism.
Consider the next verse:
Now I say unto you, if this be the desire of your hearts, what have you against being baptized in the name of the Lord, as a witness before him that ye have entered into a covenant with him, that ye will serve him and keep his commandments, that he may pour out his Spirit more abundantly upon you?
Notice the difference in wording?
In verse 10, we see the actual covenant: serve the Lord and keep his commandment. In verse 9 (and verse 8 for that matter), what read is what led the people to the waters of Mormon.
What the speaker taught is—at least in my experience—a common teaching. I have seen and heard many people teach that comforting others is something we covenant to do, but the text doesn’t support that teaching.
That being said, I’m not advocating that we have an excuse to ignore people who have burdens, mourn, and need comfort. If I’m reading the text right, it seems that these desires sound like prerequisites for baptism. And that is not something commonly taught in the church.