score:5
Calvin addresses this in his commentary on Genesis 4, arguing that Abel was already accepted by God when he made this offering:
We must, however, notice the order here observed by Moses; for he does not simply state that the worship which Abel had paid was pleasing to God, but he begins with the person of the offerer; by which he signifies, that God will regard no works with favor except those the doer of which is already previously accepted and approved by him.
A bit later, Calvin states the general principle, that everything done "before faith" is offensive to God:
All works done before faith, whatever splendor of righteousness may appear in them, were nothing but mere sins, being defiled from their roots, and were offensive to the Lord, whom nothing can please without inward purity of heart
In Calvin's thought, faith and regeneration go hand in hand β in this section, he writes "faith is a gratuitous gift of God, and a special illumination of the Spirit" β so thus we see that Calvin believed that Abel was already regenerated and saved at the time of this offering.