Exodus 32:29 (NIV)
You have been set apart to the Lord today.
Being set apart for God is to be separated from the world and its thinking. When debates and discussions arise between Christians due to carnality (1 Cor 11:19), there will be those that align themselves with the world and others with the Lord. When some challenge the validity of God's word by saying it is just a collection of good stories and that none of it is real, you will have to decide whose side you are on. Being set apart for God sometimes also means being separated from other "believers" who say Jesus is Lord but didn't believe in His power and omnipotence. They claim to be saved but do not demonstrate the fruit of the Spirit (Galatians 5:22-23). Being set apart for God sometimes requires being separated from certain churches or others in your church (Exodus 32:29, Luke 14:26) who don't believe the word of God literally but read it like a book of good rules.