Calvin on Isaiah 8:20:
Hence we learn that everything which is added to the word must be condemned and rejected. It is the will of the Lord that we shall depend wholly on his word, and that our knowledge shall be confined within its limits; and therefore, if we lend our ears to others, we take a liberty which he has forbidden, and offer to him a gross insult. Everything that is introduced by men on their own authority will be nothing else than a corruption of the word; and consequently, if we wish to obey God, we must reject all other instructors. He likewise warns us that, if we abide by the law of the Lord, we shall be protected against superstitions and wicked modes of worship; for, as Paul calls the word of God “the sword of the Spirit, ” (Ephesians 6:17), so by the word, Satan and all his contrivances are put to flight. We ought therefore to flee to him whenever we shall be attacked by enemies, that, being armed with it, we may contend valiantly, and at length put them to flight.
Source: https://www.puritanboard.com/threads/sola-scriptura.91225/, Comment 1