I'd be interested in your definition of "true sin" if social attitudes (that is, how we treat people/animals/the earth) does not suffice.  In the end we will be questioned only on the Two Great Commandments, love of God and love of our brothers and sisters.  Since God is self-sufficient, He needs nothing from us.  How then do we show our love for God?  We show our love for God by loving God's children.  That's it.  That's all.