It is interesting and shameful to note the similarities between Ancient Israel and the Church. As Scott Hahn says, "History does not repeat itself – but it does rhyme."
The Lord promises in the first reading that He will appoint one prince to bring together all the children of Israel (which is clarified in the Gospel reading as not only being the dispersed Jews, but also all the Gentile nations who are also children of God). He later promises that His servant, David (by which He means Jesus, the Son of David) shall be prince over them, but He also promises that there shall be one shepherd for them all. We do not only interpret this to mean Jesus, the Good Shepherd, but also Peter (and with him, the whole line of Popes) who is commanded by Jesus to "feed my sheep" (John 21:15-17).
Unfortunately, as with Ancient Israel, the Church has been split into multiple kingdoms and tribes. The great scandal of the Church is that it is not one as Jesus and the Father are One. Although all acknowledge Jesus as the head, the Body of Christ is divided about who will shepherd it. Even as a divided Church, the non-Christian world looks at Christianity as a force to be reckoned with (and a mighty force at that – almost a faith to be feared) – how much more effective would a united (and truly Catholic, meaning "universal") Church be at spreading the Gospel and calling together all the dispersed children of God from all the nations?
Pray that the work of re-unification may progress, so our mourning may turn to joy, as we look to the day we can celebrate with our "separated brethren" at the Eucharistic feast.