1Cor 4:6 Now, brothers, I have applied these things to myself and Apollos for your benefit, so that you may learn from us the meaning of the saying, "Do not go beyond what is written." Then you will not take pride in one man over against another.
Another way of saying "do not go beyond what is written" is "Sola Scriptura" (The Scriptures alone), which was later the cry of the Reformers over that of Catholicism and Orthodox Christianity who followed the writings of their post-Biblical theologians - their "celebrities". Nonetheless, Protestant/Evangelical Christianity has historically been involved in doing the same kind of thing. "Every word of God is flawless; he is a shield to those who take refuge in him. Do not add to his words, or he will rebuke you and prove you a liar." Pr 30:5,6
However while the Word of God - the Bible - is not to be added on in terms of content, it must be added on by way of application, but with such applications which conform to the scriptures. And in doing so one must think about the meaning, which is the point of these commentaries. But opinion must never be relegated the status of scripture.