Punctuation is one of the most important aspects of written English, and yet it is one that is taken the most lightly. It is, in fact, this feature of writing that gives meaning to the written words… much like pauses and changes in tones of the voice when speaking. An error in punctuation can convey a completely different meaning to the one that is intended.

For example:

Your book, John.

Your book, John?

Although the words are same here, the two sentences mean completely different things because of the period (or full stop) and the question mark.

The same goes here:

Don’t stop.

Don’t, stop.

The comma after the don’t has made all the difference in the meaning of the words.

Another example of how punctuation can change the meaning of a sentence:

He was bitten by a dog which hurt him.

He was bitten by a dog, which hurt him.

The first sentence means the dog hurt him. The second sentence means the bite hurts him. It’s the comma after the dog that has completely changed the meaning of the sentence.

A classic example that is generally given when teaching punctuation is the best that can be. It’s this –

Take the sentence A woman without her man is nothing. Now see the difference punctuation makes:

A woman, without her man, is nothing.

A woman: without her, man is nothing.

See how punctuation has made the same sentence mean two exactly opposite things?

It’s very important to know all the punctuation marks, their meanings, and when to use them in order to produce a good piece of writing – and more importantly, to convey the correct message.

Source: https://thewritecorner.wordpress.com/2009/11/14/the-importance-of-punctuation/