Unity, like faith, is not easily obtained or maintained. It is a continual battle to keep. Faith is essential for unity because people without faith in God rely on man's ability alone.
Unity with others must be based upon a common denominator that all hold dear, not on the perfectness of people. Why? People will never be perfect! If we give room for one another's shortcomings and focus on the perfection of God, we can work together in unity, striving together for a common goal.