Dr. John Duncan (often called "Rabbi" Duncan, due to his missionary love for the Jewish people), lived from 1796-1870. He was an amazing man, eventually becoming a professor at Edinburgh.
His genius was so striking he was once asked why he wasn't writing a book. His response, which in and of itself proves itself to be at least half true: "I cannot write, I'm just a talker."
One of his many comments that someone wrote down, that we might still ponder it today, is about Christian unity, priorities, and identity:
"I'm first a Christian, next a catholic*, then a calvinist, fourth a paedo-baptist, and fifth a Presbyterian. I cannot reverse this order."
*"catholic" here means all-embracing... not Roman Catholic, but the true church, which is not the possession of just one group of people. Rather, it's the "universal" church; it is for all people who repent of their sins and believe upon Christ.
Some more of Rabbi Duncan's thoughts on this particular theme:
"It would be well for Christendom if all the members of Christ's catholic church would endeavor to preserve the unity of the Spirit, and think oftener of the many and major points in which they agree than the few and minor ones in which they differ."
"When we all reach yonder country, we shall wonder what foolish bairns [children] we have been."
"The world is crying out for a working church and a united working church—truthing it in love."
"Seas and continents separate in space, but the church of Christ is one in him."
"The present principle that is to unite the church in the possession of the one faith is love... Love is the great inward uniting principle."
"It is a beautiful thing to see an assured and strong believer tender to weak faith, and a weak believer thanking God for his grace to the strong."
Consider Paul's exhortation to the church in Ephesians 4.1-6:
"I therefore, a prisoner for the Lord, urge you to walk in a manner worthy of the calling to which you have been called, with all humility and gentleness, with patience, bearing with one another in love, eager to maintain the unity of the Spirit in the bond of peace. There is one body and one Spirit—just as you were called to the one hope that belongs to your call—one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all."
That's seven "one's" in that last sentence.