D&C 60

12 And now I speak of the residue who are to come unto this land.
13 Behold, they have been sent to preach my gospel among the congregations of the wicked; wherefore, I give unto them a commandment, thus: Thou shalt not idle away thy time, neither shalt thou bury thy talent that it may not be known.

Because then maybe it would be too easy to become one of them?

14 And after thou hast come up unto the land of Zion, and hast proclaimed my word, thou shalt speedily return, proclaiming my word among the congregations of the wicked, not in haste, neither in wrath nor with strife.

It's a lot harder to fight with someone who won't fight...

15 And shake off the dust of thy feet against those who receive thee not, not in their presence, lest thou provoke them, but in secret; and wash thy feet, as a testimony against them in the day of judgment.
16 Behold, this is sufficient for you, and the will of him who hath sent you.
17 And by the mouth of my servant Joseph Smith, Jun., it shall be made known concerning Sidney Rigdon and Oliver Cowdery. The residue hereafter. Even so. Amen.

I don't really get the meaning of residue.