Isaiah 22:22 - Matthew Poole's English Annotations on the Holy Bible

The key; the government, the power of opening and shutting, of letting men into it or putting them out of it, whereof a key is a fit emblem; whence the delivering of the keys of a house or city into the hands of another, is a sign to signify and confirm the giving him the power and possession of it. Lay upon his shoulder; he mentions the shoulder rather than the hand, in which keys are commonly carried, either from some ceremony then in use, of carrying a key upon the shoulder, either of the officer of state himself, or of another in his name and stead; or to signify that this was a key of greater weight than ordinary, and that government, which is designed by this key, is a heavy burden, and therefore in Scripture phrase said to be upon the shoulder, as Isaiah 9:6. None shall shut against his will, or without his commission or consent.