Jamieson, Fausset and Brown on Ezekiel 4:6

6. each day for a year--literally, "a day for a year, a day for a year." Twice repeated, to mark more distinctly the reference to Nu 14:34. The picturing of the future under the image of the past, wherein the meaning was far from lying on the surface, was intended to arouse to a less superficial mode of thinking, just as the partial veiling of truth in Jesus' parables was designed to stimulate inquiry; also to remind men that God's dealings in the past are a key to the future, for He moves on the same everlasting principles, the forms alone being transitory.