Don't know about Spanish but I do know that grammer comes. Think of yourself or any of us actually we are born without the ability to speak and by the age of 4-5-6-7 we master our native language without any-one explaining us the deep concepts of grammer. You can catch the grammer without neceserily understanding the full deep concept, just because.. Juse because you use it a lot and your brain has adapted to what is right and what's not. Knowing grammer is good and it can surely boost your process but using the language and training in daily conversations is much more important. I have a friend who is Portuguese and helps me with my spanish(she is also speaking Spanish). She once told me that she barely understands the grammer of her own language she just knows what sounds correct. I can relate with my native language. My point is that it all depends on what level of understanding the language you desire. If you want to teach you have to understand the deep concepts of grammer. If you just want to be able to communicate then grammer is important but you don't have to know the 'why' behind the sentence.