Prior to the Second Coming of Jesus Christ at the Battle of Armageddon, Paul talked about a falling away or apostasy from the truth and the church of the living God.  This falling away is in preparation for the Antichrist who precedes His coming.  So, just because many individual's hearts become cold, that doesn't mean you have to let your heart grow cold.  A person needs to follow the Lord in these last days by attending church, the House of God.