Isaiah 44:3-5. “For I will pour water upon him that is thirsty, and floods upon the dry ground: I will pour My Spirit upon thy seed, and My blessing upon thine offspring: And they shall spring up as among the grass, as willows by the water courses. One shall say, I am the Lord’s; and another shall call himself by the name of Jacob; and another shall subscribe with his hand unto the Lord, and surname himself by the name of Israel.”
The first half of verse 3 can be taken in the literal sense. God has promised in other passages that He will refresh and restore the land (35:1-6; 41:17-20).
The second half is definitely a reference to a spiritual outpouring. In the future tribulation period there will be a great outpouring of the Spirit (Acts 2:16-21; Zech. 12:10-13:1) as well as in the Millennium (v. 3; 32:15).
There is no doubt that children will be born in the Millennium. They will grow in grace, and in health like grass in well-watered courses (v. 4).
Verse 5 teaches that profession of religion, recognition of Israel as God’s way of life for His people, will be common in the days of the Messiah. The line another shall subscribe with his hand unto the Lord simply means that people will write, “I belong to the Lord,” or some similar statement of identification with Messiah.