Why will God not give His glory to another (Isaiah 42:8)?

from the old testament

• In Isaiah 42:8, God says, “I am the Lord; that is my name; my glory I give to no other, nor my praise to carved idols.” Carved idols were representations of other gods or other things to worship. God is saying that He does not share His glory with any other “god.”
• In Exodus 20, we see this same sentiment. Speaking to the Israelites He had just brought out of captivity, God said “I am the LORD your God …. You shall have no other gods before me. You shall not make for yourself a carved image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth. You shall not bow down to them or serve them, for I the Lord your God am a jealous God” (Exodus 20:2–5). Being a “jealous God” means that He will not allow anything to replace Him. In other words, He will not give or share His glory with anyone or thing in creation.
• God deserves glory because He is distinct from His creation. There is an infinite distance between it and Him. He is its Creator (Genesis 1).
• God is not only distinct from creation, being its Creator, but He is also eternal, always existing (Exodus 3:14). He has no beginning or end (Psalm 90:2).
• God is also perfect (Psalm 18:30) and His thoughts are unknowable by us (Psalm 145:3).
• The Old Testament has examples of those who tried to make themselves like God and were quickly destroyed for their efforts. A key example is Lucifer who was cast out of heaven after stating his prideful intention: “I will ascend above the heights of the clouds; I will make myself like the Most High” (Isaiah 14:14).
• Satan also tempted Eve and Adam with a similar goal. They, like Satan, desired to be “like God, knowing good and evil” (Genesis 3:5). The result was death, both physical and spiritual. Not just for them, but for all of mankind (Genesis 3:19).
• Israel, for her part, often engaged in idolatry, worshiping other gods. God showed His jealousy for His glory by punishing them time and time again (Deuteronomy 32:16–21; Judges 2:12–14; Ezekiel 8:3–6).

from the new testament

• God’s jealousy for His glory never ends and extended into the New Testament. James 4:4–5 says: “You adulterous people! Do you not know that friendship with the world is enmity with God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God. Or do you suppose it is to no purpose that the Scripture says, ‘He yearns jealously over the spirit that he has made to dwell in us’?” In this case, being an “adulterer” refers to spiritual unfaithfulness (cf., Hosea), which amounts to idolatry. James chides the idolatrous believers who are acting like the world by fighting among themselves (James 4:1–3). Idolatry is not limited to religious activities but includes any sin. This is because God is holy, and anything less than being perfect is worshiping something other than God!
• First Corinthians 8:4–6 says, “we know that ‘an idol has no real existence,’ and that ‘there is no God but one.’ For although there may be so-called gods in heaven or on earth—as indeed there are many ‘gods’ and many ‘lords’—yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist.” While idols are nothing (empty items with no spiritual power), even if we pretend that they are something, only God is worthy of our devotion. He is the Creator (“from whom are all things”). Just like in the Old Testament, we learn that “there is one God.”
• We are also told to stay away from idols and be separate from the pagan, idolatrous world (2 Corinthians 6:16–18). We learn that God desires His people to worship Him alone and to be like Him, and not the world.
• God is worthy of all glory because He alone “created all things, and by [His] will they existed and were created” (Revelation 4:11). In these and many other verses, the New Testament teaches that God remains One who will not share His glory.

implications for today

God is unlike us. While we were made in His image (Genesis 1:26–27), we were created to reflect Who God is so that He would be glorified. Romans 1:18–32 talks about what happens when we exchange “the glory of the immortal God for images resembling mortal man and birds and animals and creeping things” (Romans 1:23). The result is that we start to worship and serve “the creature rather than the Creator” (Romans 1:25). “And since they did not see fit to acknowledge God, God gave them up to a debased mind to do what ought not to be done. They were filled with all manner of unrighteousness, evil, covetousness, malice. They are full of envy, murder, strife, deceit, maliciousness. They are gossips, slanderers, haters of God, insolent, haughty, boastful, inventors of evil, disobedient to parents, foolish, faithless, heartless, ruthless.” In short, our sin grows as we replace God with something else. God’s glory simply cannot be shared because nothing else is worthy. Living for something other than God only ever leads to depravity and death (James 1:13–18).

God is rightly jealous for His glory because only He is worthy of it. In response to His holiness and His love, we must strive to place Him first in our lives (1 Peter 1; 1 John 4:7–12). This starts with salvation as no one can please God without faith (Hebrews 11:6). He sent His Son Jesus to be the perfect sacrifice for our sins, so that we could be forgiven and have a path to a personal relationship with Him (John 3:16–18; Hebrews 1:3). Through Jesus, we can start to better understand God’s glory (2 Corinthians 4:6).

Once we are saved, then we must strive after holiness (1 Peter 1:13–25). We do not do that by our own effort, but by looking to Jesus, what He did, and how to be like Him (1 John 3:1–3). We rely on the power and work of the indwelling Holy Spirit (Romans 8; Ephesians 1:3–14; Philippians 2:12–13). As we read the Bible, pray, actively participate in the body of Christ, and so forth, we are worshiping God rightly and He is transforming us into His Son’s perfect image (John 15:1–17; Romans 12:1–2; Ephesians 4; Hebrews 10:19–25).