Isaiah 28:16, Therefore thus says the Lord Yahweh, “Behold, I am the one who has laid as a foundation in Zion a stone—a tested stone—a precious cornerstone, of a sure foundation: ‘Whoever believed will not be in haste.’”
We know this cornerstone to be Jesus Christ (Ephesians 2:19-22). The tense God uses is most interesting. Jesus had not yet been born, yet Yahweh said He “has laid” the foundation—the cornerstone—in Zion. This is not difficult to fathom if you already know God exists outside of time and is, therefore, not bound to the constraints of time. God is infinite. From God’s perspective, His work in Christ on earth was—and is—already done.
What does this mean for us post-resurrection Christians? From our perspective—in our constraints of time—Christ has not yet finished preparing the place for us (cf. John 14:1-3). Yet from God’s perspective, it is already done. Christ is our sure foundation, who is building for us a place in Heaven. Christ the cornerstone is immovable. Lean on Him, and you shall not be moved.