I have had both my corneas replaced with transplants.  My left eye was repaired successfully with one graft, but my right eye proved very problematic.  We look at the Israelites returning from exile in Babylon, only to find their farmlands in very poor shape and one oppressor (the Babylonians) replaced with another (the Persians).  Malachi tells the People of God that they must be patient, that they must put their full trust in God.  I had to live with only one eye working for some time.  The Israelites had to live in far greater doubt...