I would propose to the reader this thesis: God is the fundamental definer of goodness.
Expansion of the Thesis: in being the first cause and the prime mover of all creation, God has the absolute right to dictate what is good. Higher still, as the ultimate power; the only giver of life who exists outside of the entirety of the universe, He can command anything He desires of His creation and it would be fundamentally right and good.
Side NOTE: the proof for this thesis will obviously be assuming the existence of God and the reliability of the Christian Scriptures.
Proving the Thesis
1: First Cause; the Eternal, Uncreated Nature of God
God has always been. He came up with the very concept of time and then created it when he created the universe; Genesis 1:1. In fact, in the book of Job God’s creative act (and ability to destroy – or cease to provide life for – what He created) is something HE Himself uses as an argument for His unique qualification to demand worship and obedience without need of answering any man for His deeds; Job 38 onward… Isaiah 40 bears a similar idea (verses 22 and 28 specifically mention creation and God as Creator).
Through the prophet Isaiah God mocks those who would try to compare Him to anything in His creation; Isaiah 41:21-24 and Isaiah 46.
2: Ultimate Power; the Omnipotence and Autonomous Will of God
Thus we have the beginnings of the reason why God is the standard of what is fundamentally good. He is the only being that exists within the category of “god” in the highest sense; Isaiah 43:10, 44:6-8, 45:18, 1 Corinthians 8:4-6, etc. – so there is nothing above Him. And since there is nothing higher than Him, there is nothing that restricts Him. Psalms 115:3 & 135:6, Isaiah 14:24-27, Daniel 4:34-35, Psalm 33:4-11, etc.
Put in positive terms (as the psalms listed above are) God has the capability and freedom to do whatever He wants. Be that create something, or destroy something He has created, or anything that might fall between those two realms of possibility. Psalm 104:27-30, Job 34, etc.
3: Giver of Life; Divine Ability and Prerogative
God is the very sustainer of the universe. Not simply in that He made it and made it functional, but He continues to cause it to function. (Colossians 1:15-17) Without the continued intervening, life giving power of God the very atoms that make up the cells of your body would cease to exist – let alone function properly. John 1:1-4, 5:17, Romans 11:36, 1 Corinthians 8:6, etc.
Thus, if the very universe’s existence is dependent upon God, He has the fundamental right to make whatever demands of it that He may – be it from mankind or otherwise – and because there is nothing higher than Him and He exists in a category all His own that cannot be constrained by anything outside Himself, those commands would automatically fall within the categories of “right” and “good” for the creatures to whom they are given.
4: Otherness; the Holiness and Omnipresence of God
God’s very being is entirely “other” when compared to His creatures. He is Spirit: John 4:24, Numbers 23:19… And He is eternal: Psalm 90:2, Revelation 1:8, 21:6, & 22:13…
His absolute “otherness” to His creation is expressed in His title as the Thrice Holy God: Isaiah 6:3, Revelation 4:8. Nowhere else in Scripture is this form of Hebraic emphasizer used about God. Not even in the epistle where John gives us the awe-inspiring truth of God as the very definer and giver of true love (1 John 4:16) does he use this type of triple emphasis.
And so we have touched upon the tip of the proverbial iceberg that is the fact of God.
Thus far I have done nothing to define His goodness – or examine what He has said is good – but merely have provided the reasoning and “proofs” undergirding the thesis I proposed in the outset of this post. The actual topic of God’s very attribute of goodness and what He has declared to be good for His creatures is beyond the scope of this post – except to say that the greatest good for the creature is to worship, love, and obey the God that gave them life and provided a way for that to be done in the Christ.