Apparently Jesus leapfrogged over all the things you and I might have thought more important to spread the gospel of Jesus throughout the world. But Jesus knew the most important witness of his new kingdom was his followers being unified in love and oneness. My guess is Jesus knew that when people would later see us claiming to be followers but being so divided, so argumentative, so fervent about things that divide us, our movement wouldn't be very attractive.
Later on Paul shared critical issues with the church in Ephesus and reiterated how important this is. Ephesians 4:1-6 reads,
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. There is one body and one Spirit, just as you were called to one hope when you were called; one Lord, one faith, one baptism; one God and Father of all, who is over all and through all and in all.
Here again we find another major focus of Jesus we often miss. Jesus knows people will hardly agree on anything. That even people who agree on Scripture's authority may come down on different sides of an issue. I was once reminded that a point of view is simply a view from a point, and oneness, or unity, can therefore never be based on getting someone to see from your point; instead it is love and unity amid different beliefs. And this is exactly why unity is so powerful. It's almost impossible. And because it is so difficult, Jesus would much prefer we fight for a supernatural form of love and unity instead of fighting against each other or people outside our faith.
To put it in plain terms, it's time to stop fighting against sin and sinners, other denominations, liberals, fundies, conservatives, evangelicals, or mainline denominations. It's even time to stop fighting against Catholics, atheists, Rob Bell, Oprah, Driscoll, Piper, nauseating televangelists, or any other Christian leaders you disagree with on certain issues.
I realize that Paul called out a few men for false teaching, but these men were challenging the most central teaching of the gospel regarding Jesus—the cross, or the resurrection. Yeah, these are worth putting your dukes up for, but that's about the only thing we should be fighting about if we are to be unified.
Unity can happen only when we shrink down the number of hills we will die on. And according to Paul it's a very small list. For him, it's one Lord, one faith, one baptism, one God who's got all the other stuff under control because he's over all, through all, and in all. Practically, it comes down to this: if someone claims to have put his trust in Jesus for the remission of his sins, based on Jesus' death on the cross, he is off-limits! And since we now know we should also not judge those who have not made this decision, it pretty much puts all judgment in the no-go zone! That's what unity is based on.
The Umbrella of Love
In Paul's time the church was growing in size through a wide range of ethnicities, customs, worldviews, sin propensities, and traditions; there were thousands of individual stories of people who held varying and divergent beliefs on all matters of faith and life. Paul knew there would be trouble unless he put a more important umbrella of love over all the unloving conclusions they would naturally come to.