Numbers 3:13 Because all the firstborn are mine; for on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I am the Lord.
The firstborn children of Israel were spared the night that the death angel slew the firstborn of the Egyptians. They had been delivered and redeemed by a blood sacrifice, and so now God claimed them as belonging to him.
In a similar manner, we deserved to die, but God through the blood of Christ, the innocent sacrifice, spared us. And so now we belong to Him. We are his. We are bought with a price (1 Cor 6:20), and so we should glorify God in our body and our spirit which are God’s.
I wonder how we feel about God’s claim to our lives. Do we really live our lives like they belong to Him? Or do we still try to remain in control, doing things our way? May God help us realise that we do belong to Him, and so we should live to do His will.