Some thoughts on grammar:

B.J. Chute says that “Grammar is to a writer what anatomy is to a sculptor, or the scales to a musician. You may loathe it, it may bore you, but nothing will replace it, and once mastered it will support you like a rock.”

Grammar is simply the collection of principles defining how to put together a sentence.

Grammar is like a game of chess.  Each piece of grammar has a form (e.g. the king, the queen, the knight, the rook, the bishop,  the pawns.)  Each of these forms has permissible modes of moving or functioning.       

“Grammar is the business of taking a language to pieces, to see how it works.”
(David Crystal)

Fearing or hating your inner grammar is like fearing or hating your lungs, and no more useful.

English grammar is like reading itself; it demands discipline, and it develops analytical strength.

Grammar is like music, you can hear when it’s done wrong.

For me, grammar is like vegetables. They both are the things I don't like, but have to take in for myself. I have to eat vegetables to keep myself healthy, even though I don't like them that much.

Grammar isn't a set of rules that one memorizes. It is a living, complex, evolving, thing that must be experienced, enjoyed, and accepted for what it is. In other words, grammar is much like a woman.

Grammar is like a sandpit: it gives children a chance to play with  the relations between substances and things

Without Grammar it is like trying to find one's way across country without map or signposts. 

Grammar is the system of a language. People sometimes describe grammar as the "rules" of a language; but in fact no language has rules. If we use the word "rules", we suggest that somebody created the rules first and then spoke the language, like a new game. But languages did not start like that. Languages started by people making sounds which evolved into words, phrases and sentences. No commonly-spoken language is fixed. All languages change over time. What we call "grammar" is simply a reflection of a language at a particular time.

Grammar is awareness raising, i.e. focusing learners' attention on the grammar meaning and form

Grammar is the study of the rules governing the use of a language. That set of rules is also called the grammar of the language, and each language has its own distinct grammar. Grammar is part of the general study of language called linguistics.

Grammar is a study of the laws of a language that makes sense of the words.

A grammar is minimally a device that distinguishes well- from ill-formed expressions.