“For he grows up before him.” The Messiah grew up “before God,” in the sight of God. Jesus Christ did not have a plush upbringing, and did nothing to attract the attention of the world around him, but he was always walking before God.
“young plant.” Although Jesus was the Son of God, he did not burst on the scene as a mighty tree, impressive and imposing. Instead he showed up as a young plant. Jesus did not seem special, but was vulnerable, like a young plant struggling for life.
“a root.” Here “root” refers to a descendant, as it does in Isaiah 11:1 and 10, and in Revelation 5:5 and 22:16. Jesus Christ grew up before God as a “root” a descendant of David, and “he” [the Messiah, Jesus Christ] grows up before “him” [God] as a servant [Isa. 52:13. And also as a descendant of David and of the promises made to David of an everlasting kingdom (2 Sam. 7:13, 16)]. [For more information on “root” referring to “descendant,” see commentary on Isa. 11:10 and commentary on Rev. 22:16].
“out of dry ground.” The Mediterranean climate in Israel meant that there was no rain from May to October, and the ground became hard and dry, and plants struggled to survive. There is no evidence that Jesus got “miraculous special help” growing up, but struggled like everyone else. He learned obedience from the things he suffered (Heb. 5:8).