Calvin on the work of the Spirit in Old Testament times

Amidst a discussion about the work of the Holy Spirit in the life of a Christian, Calvin makes these remarks regarding the question of how the Spirit worked in Old Testament times, in comparison to New Testament times...

But it may be asked, whether there was under the Law a sure and certain promise of salvation, whether the fathers had the gift of the Spirit, whether they enjoyed God’s paternal favor through the remission of sins? Yes, it is evident that they worshipped God with a sincere heart and a pure conscience, and that they walked in his commandments, and this could not have been the case except they had been inwardly taught by the Spirit; and it is also evident, that whenever they thought of their sins, they were raised up by the assurance of a gratuitous pardon. And yet the Apostle, by referring the prophecy of Jeremiah to the coming of Christ, seems to rob them of these blessings. To this I reply, that he does not expressly deny that God formerly wrote his Law on their hearts and pardoned their sins, but he makes a comparison between the less and the greater. As then the Father has put forth more fully the power of his Spirit under the kingdom of Christ, and has poured forth more abundantly his mercy on mankind, this exuberance renders insignificant the small portion of grace which he had been pleased to bestow on the fathers. We also see that the promises were then obscure and intricate, so that they shone only like the moon and stars in comparison with the clear light of the Gospel which shines brightly on us.

If it be objected and said, that the faith and obedience of Abraham so excelled, that hardly any such an example can at this day be found in the whole world; my answer is this, that the question here is not about persons, but that reference is made to the economical condition of the Church. Besides, whatever spiritual gifts the fathers obtained, they were accidental as it were to their age; for it was necessary for them to direct their eyes to Christ in order to become possessed of them. Hence it was not without reason that the Apostle, in comparing the Gospel with the Law, took away from the latter what is peculiar to the former. There is yet no reason why God should not have extended the grace of the new covenant to the fathers. This is the true solution of the question. [Source: Commentary on Hebrews 8:10]