We live in a kind-of “bubble” in which we sense our reality through a materialism, what we can see, feel, taste, etc. Living inside this natural sphere, all thing are considered knowable. But we are not seeing the larger picture; there is an outside, a spiritual realm. Our science is dependent on our natural senses and a kind-of circular logic. We have come to accept all things as foreseeable—not because we understand them but—because all things are explainable in a language we invented to explain them!
However, we remain wonderstruck at the absolute beauty of the world we live in but not because we are any closer to the underlining “how” of it—unless we believe in God. Birth and death, for example, remain the biggest mysteries of all; we do not cease to marvel in awe at the miracle of life itself but we can only theorize its inception. We cannot reproduce it. And if you think of it, so is the inevitability of death (That’s why “time” is so important in calculating everything discoverable; it tracks ultimate growth, movement, and decay).
But outside there is an eternity not reachable by the tools of our science and ignoring it will not make it go away or any less significant to our reality. 
Angels are outside this bubble! Try explaining to them how a baby is conceived! Physical death, time, and many other aspects of our “knowledge” we call inevitable, angels remained flummoxed by. Our science has no meaning to them—only what God does on our behalf makes any sense to them.
The Archangel Michael wears a Roman military cloak and cuirass in this 17th-century depiction by Guido Reni.
One of the biggest mysteries for them is Calvary. “The law … was given through angels,” Stephen explained [Acts 7:53]. But that was “law” not “grace” Sadly for them, they don’t know “forgiveness” and “reconciliation.” Angels mediated the law given to Moses and proffered to Israel. This made perfect sense to them since the law was in reality the very profile of divine love—of the God they knew and served. Why this love would necessitate Christ’s incarnation and death was not clear; so, for this understanding, they would need our faithfulness in serving the God they served.
It was revealed to [the prophets] … things that have now been told you by those who have preached the gospel to you by the Holy Spirit sent from heaven. Even angels long to look into these things. – 1 Peter 1:12
We are truly on display before them. “We have been made a spectacle to angels,” Paul agreed [1 Corinthians 4:9]. And we probably confuse them all too often when we “sin.” Paul, for example, urged Timothy as a pastor not to have favorites within his ministry. Angels don’t know what favoritism is.
I charge you, in the sight of God and Christ Jesus and the elect angels, to keep these instructions …do nothing out of favoritism. – 1 Timothy 5:21
Furthermore, they probably speak a different language [I Corinthians 13: 1]. Our varied theological interpretations of our faith add to their confusion [1 Corinthians 11:10]. They have existed exclusively to serve God [Job 1:6].
“Angels [are] ministering spirits sent to serve those who will inherit salvation.”
The writer to the Hebrews penned these inspired words [Hebrews 1:14 ] and these angels do a better job of it than we realize [Psalm 91:11].
We are living the mystery of our salvation. It is, indeed, a mystery to the ten of thousands of angels commissioned from the Throne of God to oversee His work in us. It behooves us to faithfully live it. If we need another reason? …for their sakes.
<= Schutzengel (English: “Guardian Angel”) by Bernhard Plockhorst depicts a guardian angel watching over two children.
