But now that you have been set free from sin and have become slaves of God, the fruit you get leads to sanctification and its end, eternal life. Romans 6:22
But now thus says the LORD, he who created you, O Jacob, he who formed you, O Israel:
“Fear not, for I have redeemed you; I have called you by name, you are mine. Isaiah 43:1
Yes we are slaves of God. We have no rights, no demands to make. He can do with us what He wants, when He wants. He said it clearly through Isaiah: “You are mine” You belong to me. You are not your own (1 Corinthians 6:19-20).
God has all rights to decide what we eat, drink and wear; whom we get married with, become friends with or share an apartment with. He can decide for us whatever He wants as He wants. He is the owner. We are His and we have no right to complain.
But as God is good and wise and kind and faithful and much more, we should rejoice to belong to Him. He will never harm us. His glory is the place where we find our happiness, our perfect joy (Psalm 43:3-4).
Moreover, to be His slaves means we are His responsibility. We are His possession. He takes care of us. We are His, so He meets our deepest needs. He provides for us.
We have no rights and no concern. If someone has to be concerned about our wellbeing, it is the Lord. We are His. He refuses no good thing to the righteous (Psalm 84:11) and we always give us good things (Matthew 7:11).