What does Revelation 7:8 mean?

This verse names the final three tribes that were sealed: the tribe of Zebulun, the tribe of Joseph, and the tribe of Benjamin. According to Jacob, Zebulun would profit from maritime trade (Genesis 49:13). Perhaps in the tribulation Zebulon will exert its influence along the eastern coast of the Mediterranean Sea.

Joseph is listed as a tribe, and so is his son Manasseh, but Joseph's other son Ephraim is omitted. In dividing the Promised Land, the tribe of Joseph was split into the tribe of Manasseh and the tribe of Ephraim. It seems the tribe of Ephraim became synonymous with that of Joseph (Numbers 1:32–33). When Jacob blessed his sons, he called Joseph "a fruitful bough" (Genesis 49:22). Perhaps he picked up this term from the fact that Joseph's son's name, Ephraim, means fruitful. Jacob lavished praise on Joseph and spoke of God's protection and blessing of Joseph. Joseph's survival at the hands of his envious brothers and his elevation from prison to Egypt's throne shows how perfectly God protected and blessed him (Genesis 37—50). God will protect and bless the tribe of Joseph in the tribulation, as well.

Jacob described Benjamin as "a ravenous wolf" (Genesis 49:27). The men of Benjamin were successful warriors but they were cruel. Saul, Israel's first king, was a Benjamite who tried repeatedly to kill David of the tribe of Judah. In the tribulation both tribes will serve God together as His evangelists.