It says that Israelite leadership will remain with Judah for a long period… ad ki yavo Shiloh, “until Shiloh comes” or “until he comes to Shiloh”.
Christian exegesis takes Shiloh as a reference to Jesus, as if the verse were saying, “Judah will be the leader until Jesus comes”.
It is true that some Jewish commentators (e.g. Rashi) give Shiloh a messianic connotation, probably connecting Shiloh with shalom, peace – and of course the advent of peace is essential to Jewish messianism.
Historically this cannot refer to Jesus since he did not bring peace, nor has Christianity, either internally nor externally.
In order to explain why the messianic prophecies remain unfulfilled, Christianity posited the idea of a second coming, but the many messianic passages in Isaiah and other books do not justify this notion.
A great deal hinges on the word Shiloh.
A useful passage to consult is Isa. 18:7 which speaks of tribute, shai, being brought to God.
The Midrash therefore suggests that our verse is saying that Judah as leader will receive homage and acclamation, and people will bring shai lo, “tribute to him”. The verse would then read something like od ki yavo shai lo.
This fits in with the parallelism of Biblical Hebrew poetry and makes sense of the verse within its own context.