What is the source of suffering in the Bible?

All circumstances, all influences that seem to be evil or against your best welfare are only apparently so—

The hidden life seeks for such surroundings as will aid it to develop and to grow in the best possible manner. The true metal, first mixed with clay, seeks the acid of suffering, and mixing and fusing with that acid is parted from the earth and shows itself in its true nature. 

When you get rid of all idea of punishment, condemnation―or even injury by your inherited tendencies―or by the evil example of others, some clouds will be removed from your vision, and confidence in the absolute fairness of your destiny, engendered.