Charles Ellicott Commentary Isaiah 37:30

"And this shall be the sign unto thee: ye shall eat this year that which groweth of itself, and in the second year that which springeth of the same; and in the third year sow ye, and reap, and plant vineyards, and eat the fruit thereof." — Isaiah 37:30 (ASV)

And this shall be a sign unto thee.—The prophet now turns to Hezekiah and, as was his custom (Isaiah 7:11; Isaiah 38:8), offers a sign in the near future as a pledge of the fulfillment of a prediction with a wider range.

It was then autumn, likely near the equinox, which marked the beginning of a new year. The Assyrian invasion had stopped all cultivation in the previous spring, and the people had to rely on the spontaneous products of the fields.

In the coming year, they would still be compelled to draw from this same source. However, within twelve months, the land would be clear of invaders, and agriculture would resume its normal course. The fulfillment of this prediction within the appointed time would then guarantee the fulfillment of the wider promise that follows.