will die the death of the uncircumcised: In the Old Testament, circumcision was the sign of God’s covenant (his special agreement) with Abraham and his descendants (compare Genesis 17:10–14). To be uncircumcised meant to stand outside that covenant relationship.
This warning means the prince of Tyre would die without any share in God’s covenant promises. He would die as one who did not belong to the people of the covenant.