Here is the declaration of the mystery of Paul's attitude to Scripture:  the principle of Bible interpretation is not in the Bible itself.  You cannot just read the text and follow the instructions: keep the law, observe the holy days, offer the sacrifices.  This is why the most devout Jewish scholars missed not only the significance of Jesus' life, but also misunderstood the nature of the Old Covenant as a preparation for the revelation of the Messiah and the initiation of the New Covenant.  Paul realized that you could read the Bible backwards and forwards, and memorize entire books, and still miss the message it contained -- as he himself had done.  Why?  Because the key to Bible interpretation is beyond the Bible, it is not the pure text as written.  There is a "filter," a secret, a principle of selectivity whereby certain passages and events take precedence over others.  And though Paul did not explictly explain to his readers what this principle is, Jesus did so in the Gospel of John:

          You diligently study the Scriptures because you think that by them you possess eternal life. These are the Scriptures that testify about me, yet you refuse to come to me to have life (Jn 5:39-40).

This was also Paul's criterion for the canonicity of Scripture: Jesus is the source of the "renewed mind" (Rom 12) that alone can understand Scripture.

          We speak of God’s secret wisdom, a wisdom that has been hidden and that God destined for our glory before time began....God has revealed it to us by his Spirit.  The Spirit searches all things, even the deep things of God.... No one knows the thoughts of God except the Spirit of God. We have not received the spirit of the world but the Spirit who is from God, that we may understand what God has freely given us....We have the mind of Christ (1 Cor 2:7-16).

          The "deep things of God" -- not mysticism, but the declared word of God in Scripture.  It is the Spirit who interprets Scripture to those who are reborn of the Spirit.

John quotes Jesus saying "It is the Spirit who gives life, the flesh counts for nothing. The words I have spoken to you are spirit and they are life" (Jn 6:63).  For Paul, it is the Spirit who gives life to the the sacred texts, while man's wisdom counts for nothing:

            Where is the wise man? Where is the scholar? Where is the philosopher of this age? (1 Cor 1:20)

            These men of intellect were all prominent under the prior dispensation, whether the Jews under the Law, or the Greeks under Plato -- but now they have been superseded by "Christ the power of God and the wisdom of God" (1 Cor 1:24).

Fittingly enough, speaking of scholars, it was the Greek mathematician/scientist Archimedes who is quoted as saying: "Give me a place to stand on, and I will move the Earth."  Paul's experience on the road to Damascus and his subsequent awareness of having "the mind of Christ" were his fixed point, from which he re-interpreted the Tanakh.   He "moved" Scripture, he probed it, he participated in a decade-long dialogue between written word, conventional interpretation and the living Spirit of Christ within his mind.  And out of this "dialectic" was born the Gospel to the Gentiles, the "mystery" of God's purposes among, not just Israel any longer, but the whole world:

            This mystery is that through the gospel the Gentiles are heirs together with Israel, members together of one body, and sharers together in the promise in Christ Jesus (Eph 3:6).