So this is what the Sovereign Lord says: "See, I lay a stone in Zion, a tested stone, a precious cornerstone for a sure foundation; the one who trusts will never be dismayed (Isa 28:16).”

In order to know what God means by "So" at the beginning of this verse, we need to have some explanations concerning the important concepts that are rather foreign to us today. First, we need to understand that this stone is associated with the stone that was laid in the Most Holy Place of the Second Temple in lieu of the lost Ark (it could be that the same type of stone was also laid underneath the Ark in the First Temple). It was by God's inspiration that this stone came to be called "shetiyyah," which was a law dictating the manner of drinking in a royal feast. When this is applied to us Christians, it signifies the new way we worship and live by being led by the Spirit of God instead of being drunk with the mind of the flesh, which is death (Rom 8:6, Eph 5:18).

Second, we need to know that a stone in the Old Testament sometimes signifies an entrance (also an exist) or a boundary between two lands. In Genesis 29, we have a story of Jacob meeting Rachel at a well, and the narrative mentions several times that the stone was to be rolled away from "the mouth of the well." Also, later, after Jacob came out of Laban's house with his family, he and Laban met together and made a covenant with each other building heaps of witness with stones. Laban said:

This heap is a witness, and this pillar is a witness, that I will not go past this heap to your side to harm you and that you will not go past this heap and pillar to my side to harm me (Gen 31:52).

These heaps were the marks of the boundary of two worlds where they could not pass from one to the other. Jesus, as Jacob did, went to one world, and on the way back from there, he placed a stone at the exit. This stone is the entrance to Hell for those who are perishing, but for those who are saved, it is the entrance to Heaven. And the difference comes merely from whether to believe or not. With all these things in mind, read Isaiah 28 again, and you will come to understand what God means by "So" at the beginning of v. 16.

Paul explains, by quoting from Isaiah 28:6 (also 8:14), how the old system of seeking righteousness by keeping the Law has changed to the new system of justification by faith in Christ who has become the foundation.

Christ is the end of the law so that there may be righteousness for everyone who believes (Rom 10:4).

In this new system, we no longer try to become righteous by the works of our flesh, but live as a righteous one by having been made such through faith in the death and resurrection of Christ. When you try to seek righteousness, you lose it. Rather you start living by accepting the reality of the righteousness that God's word says you are in Christ. However, one problem we the Gentiles often come to have is that since we were saved by faith without having really sought righteousness as the Jews did, we tend to put on the attitude of legalism later as we continue learning the Bible as if it were good and necessary to seek righteousness so that we can be proud of it. Be careful! Paul goes on to explain this change from the former system to the new one by quoting from the passage in Deuteronomy 30.

But the righteousness that is by faith says: "Do not say in your heart, 'Who will ascend into heaven?'" (that is, to bring Christ down) "or 'Who will descend into the deep?'" (that is, to bring Christ up from the dead) (vv. 6-7).

This part is rather difficult, but the key to understanding it lies in the way Paul interprets the passage in Deut 30.