In English there are many characteristics of construction which have developed over time. Some of these are easily explained and some are not. You can ask your teacher by saying the example sentence above.
Why is the word "every" necessary in the sentence?
"Why" is the question word that you want to use when asking how something works. To be necessary is to be required or needed.
I hope that this helps. :)
"Why"（なぜ）は、どうしてなのかの理由を尋ねる時に使われる疑問詞です。
to be necessary は「求められる、必要な」という意味です。
これが、役立つことを願います。
What does the word 'every' add to the meaning of this sentence?
"What does the word 'every' add to the meaning of this sentence?" is a formal way of asking the question "Why do you need 'every' in this sentence?".
By adding the word 'meaning' into our question it shows that we know it must add something to the overall question, but we are just not sure what.
"What does the word 'every' add to the meaning of this sentence?"
（「every」はなんで必要なんですか）
この文は：
"Why do you need 'every' in this sentence?"
（この文にはなんで「every」が必要なんですか）
のフォーマルな言い方です。
'meaning'（意味）という言葉を加えて、それ（every）が文に何かしらの効果を与えていることは分かるがそれが何かははっきり分からないことを表しています。
"Once in a while"; "We go out to the movies once in a while."
Every once in a while"; "We go out to the movies every once in a while."
Either of these phrases would be correct ("Once in a while" or "Every once in a while"). Both as used to say that you do something occasionally or from time to time (e.g., "We go out to the movies occasionally" or "We go out to the movies from time to time"). These two examples would be another couple of ways of saying the same thing.
これらのフレーズはどちらも正しいです（"Once in a while" と "Every once in a while"）。いずれも "occasionally"（時々）あるいは "from time to time"（同）を意味します。
例：
"We go out to the movies occasionally"
"We go out to the movies from time to time"
（私たちは時々映画を見に行きます）
この二つの例のように言うこともできます。
What is the purpose of the word 'every' in this sentence?
Is it compulsory to have the word 'every' in the sentence?
Some English grammatical rules are easier than others to explain.
Ask your teacher if she or he knows why the word 'every' is required in the sentence.
When we ask about the purpose of the word we are investigating what the word does in the sentence, why it is needed.
Compulsory: a must, has to be done.
"Is it a must to use the word every in the sentence?"
英文法のルールには比較的シンプルで説明しやすいものもあります。
なぜこの文に 'every' が必要なのか先生に質問してみましょう。
"What is the purpose of the word 'every' in this sentence?" は、その文における 'every' の役割、なぜ必要なのかを尋ねます。
Compulsory: 絶対必要なもの、しなければならない
"Is it a must to use the word every in the sentence?"
（その文に 'every' は必ず必要ですか）
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