What it means to be holy

“But just as He who called you is holy, so be holy in all you do; for it is written: ‘Be holy, because I am holy.’” 1 Peter 1:15
Many Christians don’t understand what the Bible means when it tells us to ‘be holy’. They think, ‘I don’t want to be too holy, because nobody likes people who are ‘holier-than-thou’.’ But there’s a big difference between being ‘holier-than-thou’, and being holy.
Being ‘holier than thou’ is akin to the attitude that the Pharisees had during the time of Jesus. While it is true that they were extremely diligent about keeping not only God’s Law, but also the laws of the rabbis (intended to help keep people from even getting close to breaking God’s Law), they developed an attitude of superiority because of their law-keeping. We see this reflected in Jesus’ parable about the Pharisee and the tax-collector, Luke 18:9-14. They knew they were obeying God, and they looked down on everyone else.
However, this is not what it means to be holy. The word means to be set apart for special use. “In a large house there are articles not only of gold and silver, but also of wood and clay; some are for noble purposes and some for ignoble. If a man cleanses himself from the latter, he will be an instrument for noble purposes, made holy, useful to the Master and prepared to do any good work” (2 Tim. 2:20-21). Now that we have been bought with the blood of Christ, we ought to be set apart for God’s special use. This doesn’t mean that we can’t go to work, or can’t play sport, etc. But in everything we do, we are to do it as if for the Lord (Col. 3:23).