Why is Michael considered a Saint?

I think Michael the Archangel is 'hagios' to God, meaning dedicated. Hagios also means "saint", so sure, he is a saint of God, but he is not human. He is an angel. The Roman Catholic meaning of saint corrupted the better meaning for us to remember.

Well...we're talking about saints in the Catholic/Orthodox style here.

That style of "saint" includes - basically - any heavenly being other than God that

a - responds to prayers

b - performs supernatural feats on Earth (in response to those prayers)

The majority of saints of that type are people who have died, believed to have been forgiven and believed to have received eternal life in Heaven, where they also are believed to receive and respond to prayers. However: named angels (Michael, Gabriel, Raphael) are also typically included in "the litany of saints" because they (it is believed) respond to prayer in much the same way as heavenly-human saints.

Note that in the Bible the word "saint" is used differently...but also similarly. In the Bible, the word "saint" means "holy one", and the Bible refers to devout followers of God, both (living) people and angels, as "saints". The Bible does not specifically refer to people who have died as "saints".

What scripture?Michael the archangel is an angel with high rank,one of the if not the highest ranking angel.