Fear is caused by the uncertainty of the future. Sorrow is caused by the remembrance of the past. Try to keep your thoughts in the present, for the future we will never know and the past we may never understand.
Understanding is much deeper than knowledge. There are many people who know us, but very few who understand us.
If you can't explain it to a six year old, you don't understand it yourself.
Faith is deliberate confidence in the character of God whose ways you may not understand at the time.