rise, kill, and eat.

http://lds.org/scriptures/nt/acts/10?lang=eng
9 On the morrow, as they went on their journey, and drew nigh unto the city, Peter went up upon the housetop to pray about the sixth hour:
10 And he became very hungry, and would have eaten: but while they made ready, he fell into a trance,
11 And saw heaven opened, and a certain vessel descending unto him, as it had been a great sheet knit at the four corners, and let down to the earth:
12 Wherein were all manner of fourfooted beasts of the earth, and wild beasts, and creeping things, and fowls of the air.
13 And there came a voice to him, Rise, Peter; kill, and eat.
14 But Peter said, Not so, Lord; for I have never eaten any thing that is common or unclean.

I have occasionally wondered why the Mosaic law would indicate that some animal were unclean and not to be eaten. One theory I had was that some types of animals were more prone to carrying diseases which were less likely to be destroyed by the cooking habits of the time. There may or may not be truth to that. However, since the Lord giveth no commands that are physical/temporal (Doc & Cov 29:34), there must be something more.
I do not suppose it is everything more, but at least one thing more is as a reminder to Israel of the need to be clean and pure and separate from the world.
The unclean animals represent gentile or unbelieving nations (see verses above).
The clean animals must therefore represent Israel or covenant nations.
The thought bears pondering - what else can we learn from Israel being represented by clean animals? We should only take clean things into our bodies; we should not mix or mingle or defile ourselves with the unclean. I a sure there are more, but that is enough for now.