What anxiety and consternation must have descended upon the Twelve when Jesus said, "Amen, amen, I say to you, one of you will betray me."
By dipping the morsel and handing it to Judas, Christ identifies his betrayer:
“After Judas took the morsel, Satan entered him,” John writes. “So Jesus said to him, ‘What you are going to do, do quickly.’"
Judas had been plotting some sort of betrayal of Jesus for some time; that is, by his own free will he was actively creating a space inside himself in which Satan could dwell. Now, he has become the vehicle for evil.
In this case, evil is employed to uncover the Light of all Lights. But for us, the end game of why God allows sin may not be so clear.
God is always in charge, but we have the free will and power to do all we can to never make room for evil to take up residence in our hearts and minds, guiding our hands to do humiliate, destroy or corrupt others.
What spiritual practices can we employ to keep our hearts so full of Light that evil may never enter?