Learn Hardcore Finnish: Olen kiitollinen siitä, että sinä jaksat jatkaa suomea harjoittelemalla joka päivä. - I am grateful that you keep going by practising Finnish every day.

When what you’re grateful for is a whole clause (a full sentence with a verb), Finnish usually cannot attach the clause directly to the adjective. Instead, it uses a dummy pronoun that stands for “the fact (that) …”:

Olen kiitollinen siitä, että sinä jaksat jatkaa…
= I’m grateful for that, that you manage to continue…

Here siitä is required by kiitollinen (it answers “for what?”), and the että-clause explains what that refers to.

You can sometimes drop siitä in casual speech (Olen tosi kiitollinen, että autat), but kiitollinen siitä, että… is the most natural, clear, and standard form, especially in writing.

What case is siitä, and what does it literally mean here?

Siitä is:

the pronoun se (= it / that)
in the elative case (-sta/-stä), meaning “from / out of / about”.

So siitä can literally mean “from that” or “about that”.

With kiitollinen, the elative is used to mean “thankful for something”:

kiitollinen jostakin = thankful for something
siitä = for that (thing / fact)

So Olen kiitollinen siitä, että… is like “I am grateful for the fact that…”.

What does jaksat add? Why not just että sinä jatkat suomea harjoittelemalla?

Jaksaa is one of those “untranslatable” Finnish verbs. It combines meanings like:

to have the energy for something
to cope with something
to manage to keep doing something
to not be too tired / worn out to do it

So:

jatkat suomea harjoittelemalla
= you continue practicing Finnish
jaksat jatkaa suomea harjoittelemalla
= you have the energy / strength to keep practicing Finnish

Using jaksat shows appreciation that the person doesn’t give up, even though it may require effort. It’s emotionally warmer than just stating that they continue.

Why is it jatkaa suomea, not jatkaa suomi or jatkaa suomen?

Jatkaa (to continue) usually takes its object in the partitive case when the action or process is ongoing / incomplete / unbounded:

jatkan työtä – I continue (my) work
jatkan opiskelua – I continue studying

The language suomi (Finnish) works like other mass-type nouns in this kind of context and goes into the partitive:

jatkaa suomea = continue (with) Finnish

So:

suomi – nominative (dictionary form)
suomea – partitive (used as the object here)

Using suomi without case (*jatkaa suomi) is ungrammatical; suomen (genitive) would suggest a different structure, like suomen opiskelua (“the studying of Finnish”).

What form is harjoittelemalla, and what does it mean literally?

Harjoittelemalla is the third infinitive in the adessive case (often called the MA-infinitive, -malla/-mällä form).

Verb: harjoitella – to practice
MA-stem: harjoittelema-
3rd infinitive adessive: harjoittelemalla

Its core meaning is “by (the means of) practicing” or “through practicing”.

So:

suomea harjoittelemalla
literally: by practicing Finnish,
functionally: (by) practicing Finnish.

When do we use the -malla form (like harjoittelemalla) instead of the basic infinitive (harjoitella)?

Use -malla/-mällä (3rd infinitive adessive) mainly to express means, manner, or method – “by doing X”:

Opin suomea puhumalla.
I learn Finnish by speaking.
Voit parantaa taitojasi lukemalla.
You can improve your skills by reading.
Säästän rahaa kävelemällä kouluun.
I save money by walking to school.

Use the basic infinitive when the verb is just a complement of another verb:

Haluan harjoitella suomea. – I want to practice Finnish.
Yritän jatkaa. – I try to continue.

In your sentence, harjoittelemalla tells how you continue with Finnish: you keep at it by practicing every day.

Could we say jatkaa (suomen) harjoittelemista instead of jatkaa suomea harjoittelemalla? What’s the difference?

Yes, you could, and it would be grammatically fine:

jatkaa suomen harjoittelemista
= continue the practicing of Finnish (the activity itself)
jatkaa suomea harjoittelemalla
= continue (with) Finnish by practicing it

Difference in feel:

jatkaa suomen harjoittelemista
focuses more on “continuing the practice activity”.
jatkaa suomea harjoittelemalla
treats suomea as the thing that continues, and harjoittelemalla as the method: the way you keep Finnish going is by practicing.

Both are natural; the given sentence slightly highlights Finnish itself as something you “keep up”.

Why do we say joka päivä and not joka päivää or something else?

Joka päivä is a fixed, very common time expression meaning “every day”:

joka
- singular noun (no case ending)
  → joka päivä, joka viikko, joka kuukausi

It looks grammatically singular but means “each (of the) days” → effectively plural in meaning.

Alternatives:

jokaikinen päivä – every single day (emphatic)
jokaisena päivänä – on every day (more formal / written)

But joka päivää is incorrect; joka doesn’t combine with a partitive like that in this expression.

Could we leave out sinä, and just say että jaksat jatkaa…?

Yes. Finnish almost always allows you to drop the personal pronoun when the verb ending already shows the person:

että jaksat jatkaa…
= that you manage to continue…

Including sinä adds emphasis on “you”:

että sinä jaksat jatkaa…
≈ “that you (of all people / even you) manage to keep going”

So:

Without sinä: neutral, normal.
With sinä: slightly more personal, maybe admiring or contrastive.

Is the word order suomea harjoittelemalla fixed, or could we say harjoittelemalla suomea?

Both are grammatically correct:

suomea harjoittelemalla joka päivä
harjoittelemalla suomea joka päivä

Finnish word order is flexible. In many cases:

putting suomea first can slightly highlight Finnish (“Finnish, by practicing (it) every day…”),
putting harjoittelemalla first sounds a bit more neutral (“by practicing Finnish every day…”).

In everyday speech and writing, you will see both orders. The difference is subtle; context and emphasis decide which feels more natural.

What exactly does että do in siitä, että sinä jaksat…?

Että is a subordinating conjunction, very close to English “that” introducing a clause:

Tiedän, että opiskelet suomea.
I know that you study Finnish.
Olen iloinen siitä, että tulit.
I’m happy that you came.

Here it introduces the content clause that explains what siitä refers to:

siitä = about that / for that
että sinä jaksat jatkaa suomea harjoittelemalla joka päivä
= the fact that you manage to keep practicing Finnish every day

So structurally:

main clause: Olen kiitollinen siitä
subordinate että‑clause: että sinä jaksat jatkaa…

Together they form the full meaning.