Q:

Why is there a ‘w’ in the word ‘Answer’? 

This might sound silly.  I understand ‘w’ is silent.  But what purpose does ‘w’ serve?  Why is it important to have ‘w’ in there?  Why not just ‘Anser’ like it’s pronounced? 

A:

The w is not the result of purpose but of conventional retention of previous forms.  Etymonline.com has “answer” as - Old English andswaru "a response, a reply to a question," from and- "against" (from PIE root *ant- "front, forehead," with derivatives meaning "in front of, before") + -swaru "affirmation," from swerian "to swear" (see swear), suggesting an original sense of "sworn statement rebutting a charge."  Meaning "solution of a problem" is from c. 1300. 
More generally, the parallels between the written word and the sound of the word are not rigid, or I could have written “konvennshunal ritennshun”; but I don’t, because I adhere to convention.