"I am the Lord your God, who brought you out of Egypt, out of the land of slavery. You shall have no other gods before me."
The divine existence of the Holy God requires the choosing of a people to be set apart, a holy people. God chose Israel to be his own and brought them up out of the land of Egypt and gave to them their own land. And what reason did he have for doing this? So that they might worship Him (Ex 4:23).
And so he is the LORD your God because he has chosen to be your God. He has chosen you and has rescued you out of the bondage of slavery (to sin and death) in order that you might worship Him and him alone. You were not saved by any other God nor is there any power or created thing that is able to save you in times of trouble. Call out to your friends, your family, your wealth, or your loved ones, but not a single one of them is able to save you from death.
But the LORD has defeated death and has risen from the grave! Just as he defeated Pharaoh's armies and cast them into the sea, so to does Satan now stand condemned and death powerless to hold us who are in Christ. Praise be to the Father for electing us unto eternal life!