Jamieson, Fausset and Brown on Isaiah 22:22

22. key--emblem of his office over the house; to "open" or "shut"; access rested with him.

upon ... shoulder--So keys are carried sometimes in the East, hanging from the kerchief on the shoulder. But the phrase is rather figurative for sustaining the government on one's shoulders. Eliakim, as his name implies, is here plainly a type of the God-man Christ, the son of "David," of whom Isaiah (Is 9:6) uses the same language as the former clause of this verse. In Re 3:7, the same language as the latter clause is found (compare Job 12:14).