"The condition of the covenant was perfect obedience [Hosea 6:7]…. The obedience required, was a regard to the whole Law of God – that Law which was written on man's heart at his creation." Compare Romans 1:20f & 2:14f with Exodus 20:3-12f.
"With respect to the nature of this obedience, it was necessary that it should be – 1. Perfect in respect of its principle…. 2. Perfect in parts…. 3. Perfect in degrees…. 4. Perfect in duration (without interruption while God should continue him in the state of trial). Galatians 3:10….
"Our first parents were left to the freedom of their own will…. They [could] freely choose good, through a principle of grace implanted in them by the Spirit of God…[though] being created mutable."