But since there are countless effects from everything that happens, and these extend indefinitely into the future, we cannot know the whole why about something hard that has happened. Not on earth.
Here on earth, however, we can see some of the reasons hard things happen. Sometimes a hard thing gets us a good thing, and sometimes right away. Sometimes hard things teach us a greater appreciation for good things when finally they come.
Of course, God is always using hard things to teach and form us. Perhaps, in order to form us, God needed us to struggle with powerlessness and pain. Perhaps, in order to make us struggle, He needed us to deal with life's seeming randomness or lack of justice.
What is more, in every hard thing that happens, God is giving us an opportunity for faith in Him and His plan for our lives.
If we accept these opportunities, we need no longer to wonder why. We have made our own explanation.
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We do not believe in God's plan because we can always see its wisdom. We believe in God's plan because we believe in God.