To fall short of the glory of God is to sin. (“All have sinned and fallen short of the glory of God.” –Paul of Tarsus)
Here’s another quote from Paul of Tarsus: “The wages of sin is death . . .” The payoff for sin (falling short of the glory of God) is separation from the God who is the source of life. All humans have earned and deserve separation from God.
“. . . but the gift of God is eternal life.” However, God, through the death and resurrection of Jesus Christ made a way for all who have fallen short to be reconciled to Him forever.
A grasp of the truth shows us that our only access to God is ongoing repentance and obedient trust in Christ. Like the sinner mocked by the Pharisee, God’s light shows us our need to continually pray the Jesus Prayer from the depths of our heart: “Lord Jesus Christ, Son of the Living God, have mercy on me a sinner.”