That's a little bit misleading, they're supposed to determine the facts based on the evidence, then provide a verdict.

When giving a verdict they can take into account the severity of the penalty and the circumstances of the crime.

I think a jury should hear the motivation for the defendant's actions: as a counterexample consider a defendant on trial for breaking their parole (under freedom of movement), but who did so to rescue people from a burning building. A jury would have to hear the motivation to take this into account.

Disagree. Juries are there to determine justice, not facts, as much as our legal system would like you to believe otherwise.

Why would you need a jury to determine facts?

Yes they should.