Relativism 

Going back to pre-Christian times, religion was defined as giving God what is owed to Him. As such, religion’s “biggest headache” is always the perennial problem of idolatry: of giving to any created reality the love and attention that is owed to God alone.

In modern times, the greatest “idol” is that of relativism. While we might not know it by this name, this phenomenon is incredibly common. It is the view that everything is dependent on one’s personal whims; that there is no such thing as truth or objective reality, but only opinion. Further, it is the mentality behind asking, “What’s in it for me?” instead of asking the greater question, “What shall I return to the Lord for all that He has done for me?” (Psalms 116:12).

This existential narcissism is a barrier to God, because so long as we worship ourselves, we can’t worship Him.