Video from The Thomistic Institute
"If God is, why is there evil? But if God is not, why is there good?” -St. Augustine We can be sure that God only permits evil for the sake of some much better and higher good, including not only our individual good, but the good of the whole creation. Aquinas cites several of these higher goods in response to the problem of evil, not the least of which being God’s permittance of sin so that he can manifest His goodness in an even greater way as our savior. This is a beautiful and high truth that reaches its pinnacle in the cross. There God Himself takes the whole weight of our sins upon His human shoulders and bears them through terrible suffering, even unto death. He does this precisely so that his redeeming mercy and love for us sinners would shine out more clearly. The Problem of Evil (Aquinas 101) - Fr. Dominic Legge, O.P." from video introduction.