“In these last days He has spoken to us in the Son” (Heb 1:2). This is the other part of the comparison, the Son, that is, the Son of God.
Therefore, he says, we must give greater attention to what we have heard from the Son of God, “lest at any time we drift away,” lest, by failing to attend to it more, we fall away and perish.
But since the same God spoke both in the prophets and in His Son, why is greater attention needed for the words of the Son than for the words of the prophets?
Because the prophets were servants, while the Son is Master. Because the prophets spoke figuratively and shadow-wise, for “the Law had a shadow of the good things to come, and not the very image of the things” (Heb 10:1). But the Son spoke the truth of things plainly.
Because the Law “can never make those who draw near perfect” (Heb 10:1). The evangelical preaching gave perfection to the Law and to the proclamations of the prophets.
Therefore the God-man said: “Do not think that I came to destroy the Law or the Prophets. I did not come to destroy, but to fulfill” (Mt 5:17).
Because the preaching of the prophets is only a tutor unto Christ, while what Jesus Christ taught grants us salvation.
From this it is clear that what the Master Himself taught, and what He clearly commanded, being most perfect and saving, requires greater attention than what was proclaimed enigmatically by servants. That was imperfect and only preparatory to the truth.
Such an apostolic testament was very fitting for those who then had believed in Christ yet remained attached to Jewish customs. They regarded the prescriptions of the Law as equal to the evangelical legislation.