The nearer Christ comes to a heart, the more it becomes conscious of its guilt; it will then either ask for his mercy and find peace, or else it will turn against Him because it is not yet ready to give up its sinfulness. Thus He will separate the good from the bad, the wheat from the chaff. Man's reaction to this Divine Presence will be the test: either it will call out all the opposition of egotistic natures, or else galvanize them into a regeneration and a resurrection.
At its core, sinfulness is selfishness. It's enthroning yourself - your desires, your needs, your plans - above all else. You may still seek God, but you don't seek Him first. You seek Him second or third or seventh. You may sing "Jesus at the center of it all," but what you really want is for people to bow down to you as you bow down to Christ. It's a subtle form of selfishness that masquerades as spirituality, but it's not Christ-centric. It's me-centric. It's less about us serving His purposes and more about Him serving our purposes.