Falling Short of God's Glory

I struggle with doubts about the Bible and my salvation. In my studies to work through these doubts, the verse I have been using to define sin is Romans 3:23, which has the phrase "fall short of glory of God." But I can't figure out exactly what that phrase means. Can you help?
The phrase "fall short" means all sorts of things, depending on the context; it does not have one consistent meaning throughout the Bible. When you find phrases like "fall short" and "miss the mark" in passages where the Bible talks about sin, you have to look at what mark you are missing, or of what you are falling short.

In Romans 3:23, one commentary says this about falling short of God's glory:
The reason all must come to God through faith in Christ is that "all have sinned and fall short of [or 'lack,' as in Mark 10:21] the glory of God." This glory cannot be eschatological, as in 5:2, since even believers, for whom the sin problem has been solved, lack the future glory now. The suggestion that the glory is God's approbation or praise (Denney) is unlikely, since this meaning of doxa, common in Luke, is somewhat rare in Paul. C.H. Dodd seeks to link the glory with the image of God in man (cf. 1Cor 11:7) that is marred by sin. This is suggestive, but it would be more acceptable if Paul had used the past tense ("have fallen short") to match the sense in the previous statement about sin. Possibly the best interpretation is to associate the glory with the divine presence and the privilege man originally had of direct communion with God. This ever-present deprivation is depicted in the restriction of the glory to the holy of holies in the tabernacle and the denial of the right of access to the people save through the high priest once a year. God's glory is the majesty of his holy person. To be cut off from this fellowship is the great loss occasioned by sin" (EBCNT, Romans, published by Zondervan).
The bad news is that you and I lack access to God's glory. We all have sinned; we are sinners in Adam (Romans 5:12-19) and we all personally sin. The good news is that Jesus came and died to give the elect sinner access to God and his glory:
"Therefore, since we have been justified through faith, we n have peace with God through our Lord Jesus Christ, through whom we have gained access by faith into this grace in which we now stand. And we rejoice in the hope of the glory of God" (Rom. 5:1-2).
The Gospel is difficult to believe because it is so fantastic. God has, though Christ's great work of atonement, given peace and access to God's favor, God's grace.

If you have trouble believing this fantastic truth, join the club. You do not believe the Gospel perfectly, but do you believe it more than you used to? And do you desire to believe it more and more? These are good signs that though you fall short of God's holy commands, you have God's Spirit in you, prompting you towards greater sanctification.

Answer by Rev. Robert Barnes

Rev. Robert Barnes is a minister in the PCA and the Managing Editor for Bright Media.