Master & ruler

The slave who was a spoil of war was known as a 'servus,' one whose life had been preserved by his master. 

Such a servant owed his life to his master, and was thought of as endebted, therefore, for a lifetime of servitude. Hence the servant had a debt of gratitude to his master because the servant was beneficiary of his master's being a 'first giver.' 

God spares the lives of the Children of Israel, and, unlike Pharaoh, preserves their lives while taking the lives of Egypt's ruling elite. Thereby does God serve as 'first giver' not only to all of Creation but also particularly, political/economically and ideologically to Am Yisroel. On account of that beneficence, God is Am Yisroel's master. He also extracted Am Yisroel from the house of servitude, and, on that account He is Am Yisroel's ruler. 

So God owns Am Yisroel; He also owns the land of Eretz Yisroel; and He rules over Bnei Yisroel even in their own autonomy.