Deuteronomy 29:29:

The secret things belong unto the LORD our God: but those things which are revealed belong unto us and to our children for ever, that we may do all the words of this law.

See also:

What Can You Say to Someone Who Just Lost a Loved One to Sickness?
Why Does 1 Samuel 1 Say Twice that THE LORD Had Shut Up Hannah’s Womb?
Objection: Preaching Divine Healing Shipwrecks the Faith of Many