Learn Hardcore Italian: Entriamo in chiesa insieme.

Entriamo is the first-person plural form of entrare in the present tense, so it literally means we enter / we are entering / we go in.

It can also function as a first-person plural imperative:

Entriamo! = Let's go in!

So in this sentence, context decides whether it is:

a statement: We go into church together
or a suggestion/invitation: Let's go into church together

Why is there no word for we?

Italian often drops subject pronouns because the verb ending already shows who is doing the action.

So:

Entriamo already means we enter / we go in

You could say Noi entriamo, but that adds emphasis, contrast, or clarity:

Noi entriamo, loro restano fuori. = We go in, they stay outside.

In a neutral sentence, leaving out noi is completely normal.

Why is it in chiesa and not alla chiesa?