Held safe from reach or harm by something standing between. Protection implies a protector.
Latin protegere (to cover in front, to shield): pro- (in front) + tegere (to cover); to be protected is to have something placed bodily between oneself and harm.
Held safe because something stands between a thing and what would reach it. The root is literal — a cover placed in front — and it is why protection always implies a protector doing the standing-between.