Spelling is important in English. Spellings make the language very colourful and interesting. You will come across words that have spellings which make use of letters in the written form but these letters are not used in pronunciation. For instance, LAUGH is pronounced with an F sound and does not make use of the sounds related to the letters U, G and H. You will find many such words with silent letters.
Spellings become important because words are formed from letters. All of us know our English alphabet but that is not enough! Since words are formed from letters these words must be standardised so that anyone who knows English can communicate in that language. Imagine a situation where there are no accepted spellings and no grammar. It would be chaos! None of us would be able to understand what anyone else is saying. English as a language would be dead. In order to preserve the sanctity of the language certain rules must be followed and spelling of words is one such rule.