Psalm 133:1, "Behold, how good and how pleasant it is For brethren to dwell together in unity!"
This is probably the most oft-quoted Scripture on unity. I believe unity is a God thing and can change, not only our life, but the lives of those around us.
However, look at that Scripture again. It is pleasant for BRETHREN to dwell together in unity. My brother and I are a part of the same family. The same thing goes for my spiritual family. I can have unity with those of the same faith, Christianity. However, it is kind of hard to have unity with someone who doesn't believe in the same God as me. It is hard to have unity with someone who doesn't believe Jesus Christ is the Son of God.
Coffee, yes! Unity, No!
Ephesians 4:1-3 As a prisoner for the Lord, then, I urge you to live a life worthy of the calling you have received. Be completely humble and gentle; be patient, bearing with one another in love. Make every effort to keep the unity of the Spirit through the bond of peace.
Let's be honest. God's children have not always modeled unity. It is hard to convince the world Jesus loves them when we can't even demonstrate that to someone from another denomination! Jesus ate with sinners and yet, I see pastors who can't share a coffee with one another!
Romans 15:5-6 May the God who gives endurance and encouragement give you a spirit of unity among yourselves as you follow Christ Jesus, so that with one heart and mouth you may glorify the God and Father of our Lord Jesus Christ.
There is the key...following Christ Jesus. If we, the followers of Christ, would focus on what we share instead of where we DENOMINATIONALLY differ, I believe God would be glorified even more.