Grow in Grace
Luke 9:55 "But he turned, and rebuked them, and said, Ye know not what manner of spirit ye are of."
Jesus was constantly being accused of breaking the law of Moses. He taught differently than the law of Moses (Matthew 5:21-48), and now He rebukes His disciples for desiring to do what an Old Testament prophet did with God's blessing and power. However, Jesus didn't come to destroy the law but to fulfill it.
Jesus came not to destroy men's lives but to save them (John 3:16; 10:10).
"God was in Christ, reconciling the world unto himself, not imputing their trespasses unto them" (2 Corinthians 5:19). Jesus was just in doing this because He bore our sins (Isaiah 53:4-6) and the accompanying wrath of God (Matthew 27:46; Hebrews 2:9). Jesus didn't reject God's judgment against sin; He bore it (2 Corinthians 5:21). Therefore, He was able to extend the grace and mercy of God to those who would have been doomed under the law of Moses (Acts 13:38-39).
The Old Testament law was like a judge passing sentence upon sin. Jesus became our advocate (or lawyer). Even more than that, He became our substitute, bearing "our sins in his own body on the tree" (1 Peter 2:24).
He didn't destroy God's judgment; He fulfilled it in Himself, so that we could go free. This forever changed God's dealings with sinful man. In light of what Jesus has done in the New Covenant, we would be rebuked for trying to release God's wrath upon others as was done in the Old Covenant. Likewise, if Jesus would have been on the earth in His physical body, reconciling the world unto Himself in the days of Elijah, then Elijah would have been rebuked for his actions, as recorded in 2 Kings 1:9-15. There is a difference between Old Testament law and New Testament grace. "For the law was given by Moses, but grace and truth came by Jesus Christ" (John 1:17). Grow in grace.