"If God is good, why is there sin and evil in the world?"
We know that in all things God works for the good of those who love Him.
The Christian faith is the only faith that addresses the question of evil. The Bible tells us how evil entered the world: through Adam and Eve's sin in the Garden of Eden (see Romans 5:12). It tells us how sin has left its ugly mark not only on our souls but also on creation as a whole, resulting in illness and disease, earthquakes and storms, death and suffering (see Romans 8:20-22). But it also tells us how God dealt with that sin and its consequences once and for all: through the sacrifice of His Son.
God provided a solution to sin, evil, and suffering when His Son Jesus left the glories of heaven and came to earth, living a sinless life, dying on a cross, and rising again, reclaiming what Adam and Eve lost to Satan. And from the time of Jesus on, anyone who wants to have power over sin, suffering, and death can come to Jesus and receive grace—not just in this lifetime, but forever in eternity with Him.
The best response to the question of evil is not "Why God?" but "How could God be so good that He would send His Son to save me?" Moreover, we can take heart because we know that in all things God works for the good of those who love Him.