Remember that you do not need to learn grammar like a professor or researcher! In fact, the core grammar rules are very limited. If you want to learn all those grammatical phenomena one by one in the sea of textbooks, yes, you will never finish learning. But never forget that your aim of learning grammar is to understand the sentence and article, not grammar itself. Remember that native speakers usually know little about grammar. Then why should learn grammar? Because native speakers learn the language by being immersed into the environment from Childhood, and by forming the "language sense" in so strong a language environment. But for non native speakers who have no that environment, grammar is the quick way, because grammar is the summary and essence of a language, it is the formula with which you can make unlimited sentence with limited words. Notice that the formula is not so hard, and the core part of grammar is really a small part. What is hard is those "phrase", "idioms", "slang" and other conventional expressions.
Belinda