This is the 352nd most frequent Japanese word.
すべて
All; everything.
すべての modifies and emphasizes that it applies to all people, indicating inclusivity.
すべての人々が平和を願っています。
Everyone wishes for peace.
すべてが functions as the subject of the verb, encompassing all possibilities.
彼女はすべてが可能だと思っています。
She thinks everything is possible.
すべてを serves as the object of the verb, indicating comprehension of all aspects.