She'll go sit in Thekla's pew, since she was invited.

Thekla's pew contains Thekla and maybe-probably her grandparents.  Most of the people in the congregation are older folks, though not most by very much; there are plenty of younger adults and scatterings of children.  Catherine isn't the only baby.

And Rebecca might not be the only magical girl.

That's... promising for her love life if she takes the plunge? Why the little devil horns though.

The little devil horns seem to be the main nonhuman feature!  She doesn't have anything else that Rebecca can see, at least from across the aisle and a few rows down.

"Any demons who can walk on hallowed ground are welcome in Reconcilist churches," Thekla whispers when she sees where Rebecca's looking.  "That's why we're called that."

"Wait so she's actually a demon? I wasn't sure... why can she walk here?"

"Approximately because she's not going to hurt anyone anymore."

"Wow. I don't think that happens where I'm from but I guess God knows better than me."

"It only started happening a few years before I was born and it sounds like your world is farther back than that."

"Like with the plastic? Yeah, I guess."

Thekla nods as the processional's final cadence plays.

Mother Dedemos is at the sanctuary's podium.  "Good morning," she announces, and her voice sounds like it's coming from around the entire room.  People mutter 'good morning's back to her which sound normal for a space with nice acoustics.  "'The heavens proclaim the glory of God; the skies display Her craftsmanship.  Day after day they continue to speak; night after night they make Her known.'  These are the words of David in Psalms."

"Amen," says the congregation.

"Because of a miraculous healing that occurred this morning, our first song will be number 362, 'The Blood of Mirkes'." (Some people take a hymnal out of the back of the pew in front of them and start paging through it to mark the relevant song with the ribbon bookmark tucked into the spine.)  "Welcome, Rebecca."

Wave.

Next everyone reads the Creed from the program.  As with the last time she looked at it, it's really easy to understand and she can read through it way faster than she's used to being able to do with text.

Rebecca is not really self-aware enough to notice this. She's not a hundred percent on actually reciting the thing, so she just reads along silently.

Singing time!*  Thekla holds the hymnal for the two of them.  The sheet music isn't what Rebecca's used to but is quite intuitive regardless, and the congregation sorts itself into four-part harmony.

Should my body come to harm
I seek out the blood of Mirkes
Pain of brain or heart or arm
I seek out the blood of Mirkes
Oh, precious is the flow
That heals each slash and blow
Body whole that soul may grow
By the blessèd blood of Mirkes

Pill or syringe, surgery
All start with the blood of Mirkes
Maps of every artery
All start with the blood of Mirkes
Ease pain that we may learn
The body's every nook and turn
Hᴇʀ work let all discern:
Knowledge through the blood of Mirkes

Duty is not His alone
I add to the blood of Mirkes
Let the pools be overflown
I add to the blood of Mirkes
Red mantel, be my shawl
Donation my gift and call
Healthy I and we and all
My blood is the blood of Mirkes

When my time on Earth must cease
Comfort in the blood of Mirkes
Travel I in blissful peace
Comfort in the blood of Mirkes
Ease all the pain and strife
With which my soul is rife -

Off to the land of second life!
Ferried by the blood of Mirkes

The accompaniment chills way out for most of the fourth verse, only to return triumphantly at speed for the last two lines.

*Any similarity to real-life hymns the reader may be familiar with is a product of translation convention (and what the author finds fulfilling to write).  It's not diegetic.

These lyrics are SO WEIRD but she was healed by what was PRESUMABLY the blood of Mirkes so she will not let this get in the way of singing along.

The pew in front of them has pencils resting in stands in its back.  Thekla uses one to scrawl a bit in the program's whitespace, still singing along without looking at the lyrics.  She slides it over to Rebecca during the instrumental outro.

You could audition for the choir. ♪✧

may be!

Mother Dedemos turns to face the normal way for a priest finally.  "O Lord our God, we are Your companions and Your children, and though You made us with our own wills and minds, we turn again towards You.  In thanksgiving and in lack we seek You; in the paths of Your light we walk.  We follow You by choice.  Not by fear or threat do we gather here, but by love, and in love.  Love for you, O God, creator of the sea, the land, and the heavens, and love for each other, the community built around You, but not solely of You.  Bless this service, this meeting of hearts; bless those who participate in it and those who witness it; let it be worthy of delight and cause for reflection.  Lady of the night and day and the times between them, we pray this in Your name.  Amen."

Is everyone else saying amen? She will say it with everyone else if they are.

They are!

The lights dim to half brightness and about fifteen people (including Thekla) walk to the front of the sanctuary as an out-of-sight accompanist plays a few filler chords.

Once they're in position, facing the triple array of stained glass windows, the music fades out.  So do the lights.  It's still dark outside, with the barest hint of dawn drifting weakly through.

The singing starts quietly, with a very different chord structure from anything Rebecca's used to.  It's floaty, ethereal, and sits with dissonance for sometimes as many as several bars before resolving.  Lots of overlapping lines.  Most of it's in a language she can't understand or identify, but for just the bridge it switches back into the one she's been speaking.

O G - o - o - od
(Creator of the stars) (Creator of our hearts) (O Lady, Lady of our hearts)
O G - o - o - od, we watch
(As they shine resolute and singular) (So-o-o-o too do we form our constellations) (Connection, holy and satisfying)
We lo - o - o - ok, out
(To the east) (Your light, which we await) (The sun, too, is a star)

And see

- Dawn
(Dawn) (Dawn) (Dawn)

(And indeed, over the course of the song, the sanctuary has lightened significantly, more and more light streaming through the windows by degrees.)