Are we sons of God (Galatians 4:7), or slaves of God (Romans 6:18)?
This is a false dichotomy (they are both true), but our primary identity is as children, not servants/slaves
1. It is a false dichotomy because Scripture depicts us as both slaves and sons
If you're talking about who we are relative to the law, sin and guilt, in Christ, we are forgiven and accepted sons and daughters.
If you're talking about who or what our life is directed toward, we are servants aiming and obligated to serve someone else, not ourselves.
2. Our primary identity is children, given the overwhelming Scripture in this direction.
1 John 3:1; John 15:15; Rom 8:14-17; Gal 4:1-7.
But even though our inheritance is vast and unimaginable, we shouldn't be spoiled-rotten rich brats. We are still serving the Lord.
Deut 6:13; Rom 6:18.