Why is が used here instead of に?

Question

The following is an excerpt out of a conversation between me and my language partner. For context: 基本的には italki と同じです。時間があるときにメッセージを読んだり書いたりします。Skype の便利なところは、イラスト、写真、リンク、ファイルなど、いろいろなものを送れるところです。文章を読むだけではわかりにくいことも、イラストや写真、時にはYouTubeの動画なども使って説明することができます。モチベーションを保つためには、楽しみながら学ぶことが大切だと思います。

The sentence in question: モチベーションを保つためには、楽しみながら学ぶことが大切だと思います。

My attempt at translation: "Concerning preservation of motivation, I think it is important for having fun while at the same time studying."

So the problem here is that in the way I translated the sentence, I'd rather expect the particle に instead of が in 楽しみながら学ぶことが大切だ. So, either I misunderstood the sentence entirely or there is something about the use of が in the construction at hand which I don't know yet :D

Answer 1

To be honest your translation doesn't sound like natural English to me. "It is important for having fun"? I don't think I've ever heard that construction before. "It is important to have fun" sounds natural and is a better translation of the original Japanese, imo. As Greg suggested in the comments, I also interpreted the sentence as "I think having fun while studying is important for preserving motivation." が in the sentence is marking that phrase to be the subject, so like これが大切だ would be "this is important", the が in your sentence is marking the phrase to be defined by some adjective.