"Twelve things to know about angels" by Peter Kreeft

As today is the Feast of of Saints Michael, Gabriel, and Raphael,
archangels, here is a popular post years I am "recycling"
for those who missed it before. It is an excerpt from
Angels (and Demons): What Do We Really About Them? (Ignatius Press; 2004, sixth printing) by Peter Kreeft:

The Twelve Most Important Things to Know About Them

1.
They really exist. Not just in our minds, or our myths, or our
symbols, or our culture. They are as real as your dog, or your sister,
or electricity.

2. They’re present, right here, right now, right next to you, reading these words with you.

3. They’re not cute, cuddly, comfortable, chummy, or “cool”. They are fearsome and formidable. They are huge. They are warriors.

4.
They are the real “extra-terrestrials”, the real “Super-men”, the
ultimate aliens. Their powers are far beyond those of all fictional
creatures.

5. They are more brilliant minds than Einstein.

6. They can literally move the heavens and the earth if God permits them.

7.
There are also evil angels, fallen angels, demons, or devils. These
too are not myths. Demon possessions, and exorcisms, are real.

8.
Angels are aware of you, even though you can’t usually see or hear
them. But you can communicate with them. You can talk to them without
even speaking.

9. You really do have your very own “guardian angel”. Everybody does.

10.
Angels often come disguised. “Do not neglect hospitality, for some
have entertained angels unawares”—that’s a warning from life’s oldest
and best instruction manual.

11. We are on a protected part of a great battlefield between angels and devils, extending to eternity.

12.
Angels are sentinels standing at the crossroads where life meets
death. They work especially at moments of crisis, at the brink of
disaster—for bodies, for souls, and for nations.

Why do people think it's stupid to believe in angels?

One
reason is a mistake about themselves: the failure to distinguish
between (1) sense perception or imagination (which is a kind of inner
sensing) and (2) reason, or intelligence, or understanding. We don't see
pure spirits, and we can't imagine them. That doesn't mean we can't
know or understand them. We can see and imagine the difference between a
five-sided figure (a pentagon) and a six-sided figure (a hexagon), and
we can also intellectually understand that difference. We cannot,
however, sense or imagine the difference between a 105-sided figure and a
106-sided figure. Both look to us simply like circles. But we can
understand the difference and even measure it exactly. So we can
understand some things we can't see. We can't see qualities like good
and evil either. What color or shape or size is evil? Yet we can
understand them. We can imagine our brains, but not our minds, our
personalities. But we can know them.

Many who deny angels deny or
are uaware of the spiritual half of themselves. Angels are a
touchstone of "know thyself". So are animals.

Aren't angels irrelevant today? This is the age of man, isn't it?

Yes,
this is the age of man, of self-consciousness, of psychology. And
therefore it is crucial to "know thyself" accurately today. The major
heresies of our day are not about God but about man.

The two most
destructive of these heresies—and the two most popular—are angelism,
confusing man with an angel by denying his likeness to animals, and
animalism, confusing man with an animal by denying his likeness to
angels.

Man is the only being that is both angel and animal, both
spirit and body. He is the lowest spirit and the highest body, the
stupidest angel and the smartest animal, the low point of the hierarchy
of minds and the high point of the hierarchy of bodies.

More
accurately stated, man is not both angel and animal because he is
neither angel nor animal; he is between angels and animals, a unique
rung on the cosmic ladder.

But whichever way you say it, man must
know angels to know himself, just as he must know animals to know
himself, for he must know what he is, and he must know what he is not.

A free 80-minute lecture,"Aquinas and the Angels," by Peter Kreeft can be accessed here.