The seeds of unity and the seeds of division can often flower in the same garden.
But what does unity mean? Sameness or diversity? Orthodoxy or Heterodoxy?
Josaphat sought to show the means of unity in diversity. There are a lot of hard feelings between the East and the West built over centuries, and the struggles of the late 16th, early 17th centuries in the West did not make it seem like a port in the storm either. Many, both Orthodox and Roman, resisted any effort at reconciliation.
Trying to reconcile much less unify would be an enormous effort. But Josaphat was willing to try.
In the end, it cost him his life. The Roman Church sought out his much abused remains and brought them to be buried in St. Peter's. Though not Roman they added him to the Roman canon and sanctoral calendar. Some may find this an affront, a usurping of the correct judgement on such a heretic. But I see it as the recognition, not that he saw the light and came to the "right side" (he never did that) but that he worked to make us one as Christ calls us to be one.
As Pius XI noted: "He felt, in fact, that God had inspired him to restore world-wide unity to the Church and he realized that his greatest chance of success lay in preserving the Slavonic rite and Saint Basil’s rule of monastic life within the one universal Church." (Ecclesiam Dei)
Many want us all to be one or the other, Catholic or Orthodox - but that is not as Paul describes the Church: "For all of you who were baptized into Christ have clothed yourselves with Christ. There is neither Jew nor Greek, there is neither slave nor free person, there is not male and female; for you are all one in Christ Jesus." (Galatians 3:27-28)
Josaphat, pray that we may be one Body, one Body in Christ.
They do not belong to the world any more than I belong to the world. Consecrate them in the truth. Your word is truth. As you sent me into the world, so I sent them into the world. And I consecrate myself for them, so that they also may be consecrated in truth.
I pray not only for them, but also for those who will believe in me through their word, so that they may all be one, as you, Father, are in me and I in you, that they also may be in us, that the world may believe that you sent me. And I have given them the glory you gave me, so that they may be one, as we are one, I in them and you in me, that they may be brought to perfection as one, that the world may know that you sent me, and that you loved them even as you loved me.
-- John 17:16-23