If one may venture an illustration from personal experience: when I was in elementary school, those were the happiest days of my life until I progressed to high school. Those days really were the happiest days of my life until I went to university. Now we are really talking about the happiest days of my life— until graduation. Then, free from classwork, exams, professors— this is freedom at last! Thus, from the perspective of the age of fulfillment, elementary school, high school, yes, even university, all seem like imprisonment with teachers as the jailers. But at the time, it was possible to find joy and pleasure in each epoch. Here, then, a fuller understanding of a prior epoch is possible only from within a later epoch. In the same way, the Old Testament believer tasted rich blessings within the context of the Mosaic administration. But by comparison with the fullness of grace in Christ, they pale into insignificance. 37 Grasp this, and we come to see that Paul does not deny that there is divine glory in the law. His language is not pejorative but comparative.
Ferguson, Sinclair B.. The Whole Christ: Legalism, Antinomianism, and Gospel Assurance—Why the Marrow Controversy Still Matters (pp. 148-149). Crossway. Kindle Edition.