What does Isaiah 7:15 mean?

Isaiah is describing to King Ahaz the sign the Lord is giving to him. It involves the birth of a baby to a woman who is still, at the time of their conversation, a young maiden or virgin (Isaiah 7:14). She will soon give birth to a boy and name him Immanuel, which means "God with us."

Many scholars understand this sign or prophecy to have a double fulfillment. We know from Matthew 1:18–23 that Isaiah's words will be fulfilled in the birth of Jesus, who will be the long-promised Messiah. His words will also be fulfilled within a few years as evidence to Ahaz that God has spoken the truth about the coming destruction of Judah's enemies.

Now Isaiah adds some detail. This boy, Immanuel, will "eat curds and honey" when he knows right from wrong. It's unclear what the significance is of eating curds and honey. Some commentators suggest that the arrival of the Assyrian army in the region will lead to a change in diet for those in Judah. Isaiah may be pointing toward that. The Assyrians and Babylonians ate a form of curds called "ghee" and paired it with honey.

Isaiah's statement regarding the boy's ability to know evil from good might suggest the point where children begin to develop control over their impulses: as early as three years old. Or, this might refer to the stage where culture considered a person fully responsible for their actions, somewhere between the ages of 12 and 20. Both would fit with the historical outcome of what Isaiah is pointing to, as described in the following verses (Isaiah 7:16–17).