“Viewed properly, there is only one duty, that of love, which is the fulfillment of the law (Rom. 13:10). And there actually is only one object of that love, namely, God.
Everything else– people, angels, nature, art, and so forth– may and must be loved only in God and for God.
The sole end of all things– ourselves, our neighbor, the state, and the like– is God’s glory.
God is also the only one who obligates us in His law; He alone compels us in our conscience. A duty exists only because there is a God who can obligate us. For duty is an obligation not only to do things but also to will them.
God obligates us in such a way that we feel obligated also to have to will what God commands. People and animals can force us to do things. God alone can obligate us, can oblige us to will.
He alone is sovereign over our conscience, the Lord also of our innermost being, the Master of and in the deepest depth of our heart.
‘I am the LORD your God’ serves as a heading above all the commandments.
And for this reason, for this reason alone, we are not only to love Him but also for His sake to love our neighbor, not kill him, and so forth.
We are to love our neighbors not because they are lovable, good, beautiful, and rich, but for God’s sake. Actually, therefore, there is only one type of duty– or better: there is but one single duty– toward one object only– namely, God.
All other duties acquire force only in and through that and under that. All duties are therefore religious duties.
Thus, the nature of duty does not disclose any classification of duties; all duty is mandatory for God’s sake and at God’s behest; there are no broad, imperfect duties.
The end goal, too, offers no basis for classification; all things must be done for the glory of God.
But besides an ultimate end there is also, under God, a subordinate end (which Pietists fail to appreciate all too much). It is not an ultimate goal, yet still a relative goal, a secure stage for our conduct.
That is the creation, the world of creatures: angels, humans, nature, art, science, and so on and so forth.
They may be– nay, must be– loved in God and for God, but they are nevertheless truly objects of our love.
Therefore, God Himself classifies the law as two tables: love of God and love of neighbor (Matt. 22:37-40).”
–Herman Bavinck, Reformed Ethics, Volume 2: The Duties of the Christian Life, Ed. John Bolt (Grand Rapids, MI: Baker, 2021), 2: 101-102.