to heal: to make a sick, wounded, or broken thing sound and whole again.
At its center this word is about restoring something to soundness. A sick body, a wound, a foul spring, a cracked pot, a ruined people: in each case the word names the act of putting right what has gone wrong, so that the thing works as it should again. The everyday picture is the healing of the body, and that picture is what the other uses lean on.
From there the word stretches in two directions that are still the same idea, not different ideas. It can be used of objects and places, where to heal a spring of bad water or a stretch of useless land is simply to make it good and usable again, the way a body is made well. And it is used again and again of God restoring his people: forgiving their sin, lifting a judgment, bringing them home from exile. The prophets reach for it because the nation's trouble is pictured as a sickness, so its rescue is pictured as a cure.
The Bible names God as the great healer (he calls himself the one who heals in Exodus 15:26), yet it does not set human medicine against him. Human physicians appear without blame, and a law even assumes a man will pay to have an injured person healed. Healing can be a plain return of health, or a deep act of mercy in which God forgives, restores, and makes his people whole. Often, especially in the prophets, the physical and the deeper meaning are felt together.