Our article Evidence for Reincarnation provides extensive empirical evidence that each one of us is completely different from our physical body. We identify with the physical body when we want to forget our real transcendental nature and our original relationship with Krishna (God). Since the real nature of the self is to be constantly absorbed in an ecstatic loving relationship with Krishna, we can not actually be satisfied without this relationship.
Thus, dissatisfaction prevails in the material world, and consequently people are always engaged in looking for a way to fill the inner void residing in their hearts. Unfortunately, many avenues for prosperity and enjoyment involve exploiting others, and so we accumulate bad karma, which means negative reactions to our activities. These negative reactions take the form of war, famine, disease, injury and neglect by people we love, and thus we suffer.
The actual remedy to this situation is to seriously practice bhakti-yoga, which reawakens our ecstatic loving relationship with Krishna, and thereby provides happiness beyond our wildest dreams, not to mention giving us a superhuman body that never gets sick or old.
Bhakti-yoga has been practiced for thousands of years according to detailed descriptions given in Bhagavad-gita As It Is, The Nectar of Instruction, Sri Isopanisad, Srimad-Bhagavatam, Caitanya-caritamrta and The Nectar of Devotion.
People who do not believe in reincarnation and yet believe in the one, omnipotent, supreme God, can not explain why some children are born in horrible suffering conditions. But if we accept reincarnation, then our suffering in this life is due to bad actions we performed in previous lives. Thus, God is not whimsical or sadistic, rather we have only ourselves to blame for our suffering.
This does not mean that bhakti-yogis are indifferent to the sufferings of others; they help those in suffering conditions. But more than just helping with food relief or hospital care, bhakti-yogis know the real cause of suffering, and they know the real solution: reawakening our relationship with God. Thus, they engage in the highest welfare work, which is teaching everyone how to practice bhakti-yoga.