To a great extent, the Catholic Church shows a unity in many aspects.
We have an hierarchy with the Pope as the head of the Church.
We have a defined body of teachings.
We have a common form of worship, even though the language might be different from place to place.
So in many ways, these aspects reinforce our unity as Church.
But the unity that Jesus prayed for is not just about external uniformity.
Jesus prayed for the unity between persons and between peoples.
He used Himself and the Father as a model of that unity.
It is a unity of heart and mind; it is a communion of love.
But the human tendency is to be divided rather than to be united; to be separated than to be connected.
Jesus prayed for unity. His prayer will be fulfilled by the Spirit which binds hearts and minds in a communion of love.
And when things get messed up and even heated up as we heard in the 1st reading, then let us remember these words of wisdom (which is often attributed to St. Augustine)
In the essentials, let there be unity.In the non-essentials, let there be liberty.In all things, let there be charity.