Isaiah's Prophecy about SHL vs. Jesus
At the time of Isaiah 28 was being written, the people of Judah were looking to make an alliance with Egypt to protect them from the Assyrians. This event is spoken about nearby -- at Isaiah 30:6-7. This passage describes the Judahites going down to Egypt for aid. It is again referenced in Isaiah 31:1-3 where God condemns these same travelers for their lack of trust in God. See Carol J. Dempsey, Isaiah: God's Poet of Light (Chalice Press, 2009) at 70.
However, before these passages, at Isaiah chapter 28, we read what sounds like a prophecy about Jesus, and an enemy called SH'L -- that can be translated as SHEOL or SAUL. For vowels were not used at the time Isaiah was written, so it can be either Hebrew word. If you were to incorrectly overlay the historical events at the time, you might think this is about the people seeking an alliance with SHEOL. The grave. You might then think this is merely an allegorical name for Egypt. But is it?
However, the time and events spoken about in Isaiah 28:18 et seq are similar to Isaiah 53 about Messiah. In this passage, it is about God setting a chief cornerstone at Jerusalem -- no doubt Jesus. Let's review it as simply how it reads without trying to apply it to events that it does not record or mention -- the effort elsewhere to create an alliance between Egypt and the southern Kingdom of Judah. I think you can clearly see this is about Jesus and a prophesied opponent.
A Prophecy about Jesus & Paul?
In Isaiah 28:18, God speaks of people who have a "covenant with SHL," typically translated as SHEOL or the grave. The people falsely believe this covenant will protect them from "the whip when it passes through." This appears to be a reference to Jeremiah 30:23-24. That passage speaks about a whirl wind that passes through which represents the wrath of God on the wicked in the latter days.
Thus this Isaiah passage means these covenant-people believe their covenant with SHL gives them salvation / protection from God's wrath. Then these people whose prophets and leaders are apostate against God's Law are at odds with what God describes as something He ALREADY LAID as a "chief cornerstone" in Zion. (Isaiah 28:16; see below.) "Behold I am the one who has LAID as a foundation in Zion....a precious cornerstone." This cornerstone is obviously Christ, as Jesus / Yashua made clear in Luke 20:17. Jesus quoted this passage from Isaiah 28, and applied it to himself. Hence, Jesus tells us Isaiah 28 was a prophecy about Himself.
Thus, the contrast is between SHL and Jesus / Yahshua in Isaiah 28. Listen with ears to hear to verses 14-18 -- with SAUL placed besides SHEOL as a legitimate alternative translation:
14 Therefore hear the word of the LORD, you scoffers,
who rule this people in Jerusalem!
15 Because you have said, “We have made a covenant with death,
and with SAUL / Sheol we have an agreement,
when the overwhelming whip passes through
it will not come to us,
for we have made lies our refuge,
and in falsehood we have taken shelter”;
16 therefore thus says the Lord GOD,
“Behold, I am the one who has laid[c] as a foundation in Zion,
a stone, a tested stone,
a precious cornerstone, of a sure foundation:
‘Whoever believes will not be in haste.’
17 And I will make justice the line,
and righteousness the plumb line;
and hail will sweep away the refuge of lies,
and waters will overwhelm the shelter.”
18 Then your covenant with death will be annulled,
and your agreement with SAUL / Sheol will not stand;
when the overwhelming scourge passes through,
you will be beaten down by it.
The message then would be those relying upon a covenant with Paul / Saul, not the one renewed by the chief cornerstone Yahshua with Yahweh, have a false hope. God describes it as a covenant with death. Paulinists' agreement with Paul will not protect them when the whip of the judgment of God passes through.
What protects those who believe in Jesus / Yahshua? They won't be "in haste." They won't make hasty judgments that include Paul as a legitimate authority whose gospel of death can ever replace the true gospel of eternal life brought by the true Jesus.