If God Exists, Why Does He Allow Evil, Pain, Suffering, and Sickness?

Throughout history, a single question has plagued humanity; a question often asked about an issue that all Abrahamic religions face. If an All-Powerful God, who is All-Knowing, All-Seeing, All-Hearing, Loving, Most-Merciful, and All-Just in control of All things and matters, exists, then why do people experience evil, pain, and suffering in this world? Why must we contend with sickness, natural disasters, starvation, war, calamities, corruption, and killings? If God is Most-Merciful, All-Lovi...