Biblical holiness is separation. We are holy when we separate ourselves from the world and unto the Lord Jesus Christ. There are many saved individuals in the world today, but very few are holy because they do no separate themselves unto the Lord.
1 Peter 1:16b--"...Be ye holy; for I am holy."
This is a command and a goal from God to every believer. We are to be holy as God is holy! Although this is a command many do not live in holiness.
We should live holy because:
1) Holiness glorifies God.
2) Holiness brings a good testimony.
3) Holiness is pleasing to God.
4) Holiness shows the light of Christ though us.
5) Holiness is a good idea (it is God's idea).
6) Holiness bring blessing on ourselves and all around us.
All of these are good reasons of why we should be holy, but the number one reason is because, "It is written.." This is our instruction from God therefore, we need no other reason to live holy lives.