All the great Teachers of Ancient Wisdom have taught the reason for suffering. Jesus taught that suffering was caused by separating from the love of God, disconnecting through negative thoughts, actions, and emotions that take us away from God. Essentially, Jesus taught that falling away from our real nature, our true being, causes us to suffer. In order to connect again with our real nature, we have to love God first and love all of our brothers and sisters without exception. Jesus further elaborated the way to get back into oneness with God through the simple teachings of the Beatitudes. For example, “Blessed are the peacemakers, for they shall be called children of God.”
Buddha taught that desire causes suffering. When we do not have what we want, we long for it and this causes a burning in our being until it is satisfied. If we withdraw our attention from the object of our desire or craving, then we cease to suffer. Buddha taught this to his disciples 500 years before Jesus came.
An ancient teaching that comes from Vedanta in India describes five causes of suffering called the Five Kleshas. The first cause of suffering is not knowing the true nature of Reality. The second cause of suffering is grasping or holding onto what is illusory or insubstantial. The third cause of suffering is from an aversion to something, a fear of something, a revulsion to something that is insubstantial. The fourth is identification with the false self or ego and thus we are constricted and limited in our consciousness. The fifth cause of suffering is the fear of death. As you can figure out, all of these causes of suffering are contained in the first one which does not know the true nature of reality. Not knowing the true nature of reality is thinking and seeing things in ways that distort reality.
The teaching boils down to this: if you look outside yourself for what will fulfill you or make you happy, you are very likely to be disappointed. If you desire something outside yourself, you are suffering from a misconception about reality. All goodness and love is inside you at the core of your being where God resides. If you travel within and focus completely inside in the center of your being, you will find the love, peace and fulfillment you have been looking for. Anything outside is transitory and shallow compared with what is within. It takes courage to make the journey to the center of your being as you have to let go of the illusion of separateness or emptiness. You will stop suffering as you enter into that relationship with God and let go of the idea that you are vacuously empty. When you discover God within, all craving ceases along with any fear, revulsion, prejudice or anger. You are in peace because you lack nothing as you openly enter into the embrace of oneness with God within.