(Thoughts inspired by conversations with others on the same OU French course.)
When I went to school, grammar was not on the syllabus, it wasn't considered useful. I picked up some basics in 'O' level French, but mostly it seemed to relate to verbs and what tense they were in. I learnt what was necessary in the same way as a child eats vegetables - “because they're good for you”. And as I started learning French again, I still thought that it was a necessary evil, part of learning a language. A case of learning the rules and the exceptions, so you could move on to the interesting stuff.
To have a break from exercise books and online activities, I have been reading a book of French fables. I started this several years ago and managed about half a page each time, before giving up in frustration. Now, I find I can manage a whole story, maybe five or 10 pages. And by practising French in a different context, I suddenly understood the why of learning grammar. For some time I have been bothered by sentences where I understand most of the words and the general sense of the piece, but there are spare words. Go ahead and laugh, but despite looking each word up in the dictionary, I couldn't make out their purpose.
Studying a lesson on the word 'en', one of those troublesome little do nothing words, I started to see why it was there. It's role with the present participle, which I had seen before, but hadn't really understood either, showed me the link between understanding the rules – the grammar and comprehension of the language.
It might not make learning grammar any easier, but now it feels less like eating your greens because they 're good for you.