gyeongchiga joheunikka geuneureseo swigo dasi himnaeja.

A natural breakdown is:

• 경치가 좋으니까 = since the scenery/view is nice
• 그늘에서 쉬고 = rest in the shade, and...
• 다시 힘내자 = let’s regain our energy / let’s perk up again

So the structure is:

reason + action 1 + action 2/proposal

Korean often puts the reason first, then the main suggestion at the end.

가 marks 경치 as the subject of 좋다.

• 경치가 좋으니까 = since the scenery is nice
• 경치는 좋으니까 would sound more like as for the scenery, it is nice..., often with a contrastive nuance

In this sentence, 가 is the more neutral and natural choice. It simply presents the scenery being nice as the reason for what comes next.

-으니까 / -니까 means because, since, or so.

• 좋다 = to be good
• 좋으니까 = because it’s good / since it’s nice

Here it gives the reason for the suggestion:

• the scenery is nice
• so let’s rest in the shade and recharge

It is very commonly used when the next part is a suggestion, command, or request.

Both -아서/어서 and -으니까/니까 can express a reason, but -으니까 is especially natural when the following clause is:

• a suggestion
• a command
• a request
• a decision

Since 힘내자 means let’s..., -으니까 fits very well.

So:

• 경치가 좋으니까 ... 힘내자 = very natural
• 경치가 좋아서 ... 힘내자 = understandable, but less typical in this kind of proposal sentence

그늘 means shade.

에서 marks the place where an action happens.

• 그늘에서 쉬다 = rest in the shade

Korean usually uses:

• 에 for destination or existence
• 에서 for the location of an action

Since 쉬다 is an action, 에서 is correct here.

쉬고 is 쉬다 + -고.

• 쉬다 = to rest
• -고 = and, and then

So 쉬고 connects this verb to the next one:

• rest,
• and then regain energy

In sentences like this, -고 often links actions in sequence. It does not have to mean a long time gap; it can simply mean and then or and.

힘내자 comes from 힘내다.

• 힘 = strength, energy
• 내다 = to bring out, produce

So 힘내다 literally suggests bringing out strength, but in real usage it means things like:

• cheer up
• keep your spirits up
• regain energy
• hang in there
• let’s push on

-자 is the ending meaning let’s.

So 힘내자 means let’s cheer up, let’s keep going, or in this context, let’s recharge and keep going.

다시 means again.

Here it suggests:

• after resting,
• let’s get our energy back again
• let’s start up again

So it gives the sense of recovering and continuing. It fits the idea that the speaker and listener may be tired, will take a break, and then continue with renewed energy.

The subject is omitted because it is understood from context.

With -자, the meaning is automatically inclusive:

• 힘내자 = let’s regain energy

That implies you and I or we.

So the understood subject of both 쉬고 and 힘내자 is the speaker together with the listener. Korean often leaves subjects unstated when they are obvious.

It is casual/plain style, suitable for:

• friends
• close coworkers
• family
• people of similar status

The ending -자 is a casual suggestion: let’s ...

If you wanted to sound more polite, you would normally change the ending style, for example to a polite suggestion such as 힘내요 in an appropriate context. The original sentence, though, sounds warm and natural in informal speech.

Not really. It sounds more like a friendly suggestion or encouragement.

• 쉬어라 would sound more like a command: Rest
• 쉬자 / 힘내자 sounds inclusive: Let’s rest / let’s keep our energy up

So the sentence has a cooperative tone, not a bossy one.

It is pronounced roughly like 조으니까.

That is because the ㅎ in 좋- is not strongly pronounced before the vowel in this form.

So:

• spelling: 좋으니까
• pronunciation: approximately 조으니까

This is normal and something learners see often with words like 좋다 in different conjugations.