Same with unresolved conflict in a church (or in a family), it spreads and does damage and from the outside the "body" might look healthy, but inside there's a foreign substance eating away at the body.
Not only does it eat at the fabric of a church body, it grieves the Holy Spirit! Many times in scripture we're commanded to not have divisions and be united. Yes, there's going to be conflicts, that's why Jesus lays out in Matthew 5 and 18 how to be a peacemakers with others. It's a command to resolve conflicts!
Are there people at your church you just avoid because you don't like them?
Are there people you haven't forgiven for something they've done or said?
Are you holding onto any grudges because you think you need to be justified or defended to someone?
Are you gossiping or slandering people you go to church with?
Have you heard a rumor but not checked the facts, so your attitude towards someone is cast in a negative light?
Are you living at peace with all men, so much as it depends on you?
Are you willing to humble yourself and admit your wrong with a person who you don't think "deserves" your apology?
Oh may the body of Christ rid itself of cancer. Let it start with me, with us, and spread! I'll tell you there is absolute FREEDOM in dealing biblical with an unresolved conflict. Having conflict weighs down your heart and will effect everyone you worship with!