Lets dissect this Passage shall we ?
(We all with unveiled face) Paul here gives an invitation to every Christian. He will speak of an intimacy of relationship and a transforming power that is not the property of just a few priviledged Christians. It can belong to everyone, everyone who has an unveiled face.
How do we get an unveiled face? When one turns to the Lord, the veil is taken away (2 Corinthians 3:16). If we will turn to the Lord, He will take away the veil and we can be one of the we all.
(Beholding as in a mirror the glory of the Lord) We can see the glory of the Lord, but we cannot see His glory perfectly. A mirror in the ancient world did not give nearly as good a reflection as our mirrors do today. Ancient mirrors were made of polished metal, and gave a clouded, fuzzy, somewhat distorted image. Paul is saying "We can see the glory of the Lord, but we can't see it perfectly yet."
(There may be another thought here also) "Now as mirrors, among the Jews, Greeks, and Romans, were made of highly polished metal, it would often happen, especially in strong light, that the face would be greatly illuminated by this strongly reflected light; and to this circumstance the apostle seems here to allude." (Clarke)
Are being transformed: As we behold the glory of God, we will be transformed. God will change our lives, and change us from the inside-out. Though the old covenant had its glory, it could never transform lives through the law. God uses the new covenant to make us transformed people, not just "nice" people.
Everyone wants to know, "How can I change?" Or, everyone wants to know, "How can they change?" The best and most enduring change comes into our lives when we are transformed by time spent with the Lord. There are other ways to change (guilt, willpower, coercion), but none of them are as deep and long lasting as the transformation that comes by the Spirit of God as we spend time in the presence of the Lord.
Yet, it requires something. It requires beholding. The word means more than a casual look, it means a careful study. We all have something to behold, something to study. We can be transformed by the glory of the Lord, but only if we will carefully study it.
Into the same image: As we look into "God's mirror," we will be changed into the same image of the Lord. When we spend time beholding the glory of the God of love, grace, peace, and righteousness, we will see a transforming growth in love, grace, peace, and righteousness.
Of course, this is how you can know someone is really spending time with the Lord: they are being transformed into the same image. But much depends on what we "see" when we look into "God's mirror." In this analogy, "God's mirror" is not a mirror that shows us what we are as much as it shows us what we will become, and what we will become is based on our picture of who God is. If we have a false picture of God, we will see that false picture in God's "mirror" and will be transformed into that image - much to our harm, both for now and eternity.
Not everyone sees the truth when they look into the mirror. 30 year old David gets up every morning, and his morning routine only gets as far as the bedroom mirror, where he sees a horribly distorted face - a crooked, swollen nose covered with scars and a bulging teye. The pain from his deformities caused him to quit college and move in with his parents ten years ago. Since then, he has rarely left his room, afraid to let anyone see him. He has had cosmetic surgery four times, but with no progress. That's because the problems with David's appearance are only in his mind. Experts call it body dysmorphic disorder, or BDD. It causes people to imagine themselves as deformed, ugly people. Psychiatrists call it a hidden epidemic. One psychiatrist says "Patients are virtually coming out of the woodwork. I'm meeting with one new patient each week." Most BDD suffers are convinced the problem is with their face. Those afflicted live with such an overwhelming sense of shame that they can barely function. One young teacher in Boston tried to continue her job but would run out in the middle of class, afraid that her imagined hideous appearance was showing through her thick makeup. A Denver businessman called his mother from the office 15 times a day for reassurance that he did not look grotesque and spent hours in the bathroom stall with a pocket mirror trying to figure out a way to improve his appearance. Some try to cope with harmful rituals, and cut themselves to "bleed" the damaged area. BDD sufferers are usually convinced that the problem is with their body, not their mind. They don't want to see anybody but plastic surgeons and dermatologists for their problem.
But when we behold the the picture of God as He is in truth, we will be transformed into His image. This is God's great design in our salvation, for whom He foreknew, He also predestined to be conformed to the image of His Son (Romans 8:29). Calvin speaks to this great design of God: "that the image of God, which has been defaced by sin, may be repaired within us … the progress of this restoration is continuous through the whole of life, because it is little by little that God causes His glory to shine forth in us."
(Are being transformed) This work of transformation is a process. We are being transformed. It isn't complete yet, and no one should expect it to be complete in themselves or in others. No one comes away from one incredible time with the Lord perfectly transformed.
(From glory to glory) The work of transformation is a continual progression. It works from glory to glory. It doesn't have to work from backsliding to glory to backsliding to glory. God's work in our lives can be a continual progression, from glory to glory.
(By the Spirit of the Lord) With these last words, Paul is emphasizing two things. First, this access to God and His transforming presence is ours by the new covenant, because it is through the new covenant we are given the Spirit of the Lord. Secondly, this work of transformation really is God's work in us. It happens by the Spirit of the Lord, not by the will or effort of man. We don't achieve or earn spiritual transformation by beholding as in a mirror the glory of the Lord. We simply put ourselves in a place where we can be transformed by the Spirit of the Lord.