Both sanctification and holiness imply being "different" or "set apart" for a special purpose. God instituted His law of clean and unclean to show the difference between His people and the nations around them. Paul calls the church "the Israel of God" (Galatians 6:16). I Peter 1:13-16 shows very clearly that Christians, spiritual Israelites, now have a responsibility to be holy as God is.
Clean and Unclean Meats
Verse 2, though similar to verse 1, goes in a slightly different direction, revealing Israel's status with God. He called them a special people, set apart as God's chosen. In similar fashion, God regards His people today, the church, as His own special people (I Peter 2:9). These two verses show that God had a special purpose for Israel, one of being an example to all the peoples around them, and thus their appearance and behavior were important. In modern terms, God does not want His people to follow worldly practices such as radical hairdos, cult fashions (Goth, grunge, gang-banger styles, etc.), tattoos, body piercing, and the like. God wants His chosen people, set apart for a special purpose, to know who they are and that what they do to the outside of their bodies is important to God.
Whatever Your Heart Desires
Other Forerunner Commentary entries containing Deuteronomy 14:2: