I will pour water My Spirit, as it is expounded in the latter part of the verse, frequently compared to water in the Scriptures; upon him that is thirsty That is destitute of it, and that sincerely and earnestly desires it; and my blessing upon thine offspring All the blessings of my covenant, especially those of a spiritual nature. This promise seems to have been made with a design to raise the minds and hearts of the Jews from carnal and worldly things, to which they were too much addicted, to spiritual and heavenly blessings, and thereby to prepare them for the reception of the gospel. And they shall spring up, &c. They shall increase and flourish like grass, and those herbs and plants which grow up in the midst of it. One shall say, I am the Lord's, &c. This verse seems to relate to the increase of the church by the accession of the Gentiles: as if he had said, The blessing of God upon the Jews shall be so remarkable that many of the Gentiles shall join themselves unto them, and accept Jehovah for their God, and own themselves for his people.
Related Commentaries of Isaiah 44:3
Isaiah 44:3-5
3 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:
4 And they shall spring up as among the grass, as willows by the water courses.
5 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.