Summary
For God was pleased to have all His fullness dwell in Him, and through Him to reconcile to Himself all things, whether things on earth or things in heaven, by making peace through the blood of His cross. - Colossians 1:19-20, BSB
God reconciled all things, both on earth and in heaven, to Himself through Jesus and the blood of his cross.
Biblical Support
Explanation
Why does Paul say that Jesus reconciled things in heaven to God?
I thought Jesus’ sacrifice was to save people. I thought there was no hope for the demons. Is this related to the groaning of the whole creation due to sin entering the world?
All of creation was affected by sin. Through Jesus’ blood on the cross, He has reconciled all things, both in heaven and on earth, to Himself.
Not all human beings will be reconciled, so this isn’t literally all things. This is a figure of speech expressing the comprehensive scope of God’s work, not a literal statement that every creature will be reconciled.
Unbelievers and those who do not receive Jesus will not be reconciled. They will perish. Similarly, the fallen angels will not be reconciled. But all powers in heaven and earth will be brought under His rightful authority, through willing submission or through judgement.