I agree with some of the other comments in the post, but the analogy falls through here. Certainly we can see ourselves in the mirror, but the reference to "seeing face to face" in Heaven is without a mirror. If the reference is to seeing Christ Jesus, who is the Spirit of prophecy, then it makes perfect sense. But if it is a reference to seeing ourselves face to face, and without a mirror... that's kinda existential, don't you think?
Existential? Not sure what you mean.
Seeing face to face would be speaking of "not in an enigma", going back to Moses. God spoke with Moses face to face, but to others in enigmas, what that right? If Paul has that passage in mind, and he's thinking, not in enigmas, the opposite, face to face.
But I'm really thinking beyond that too.
2 Corinthians 3:18, that other mirror passage, well, starting back a bit,
15 But even unto this day, when Moses is read, the vail is upon their heart.
16 Nevertheless when it shall turn to the Lord, the vail shall be taken away.
17 Now the Lord is that Spirit: and where the Spirit of the Lord is, there is liberty.
18 But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the Lord.
Where do we most see Jesus? In this world?
Until the heart turns to the Lord, we don't see Him at all. And not seeing Him, we truly do not see ourselves. "It is not yet revealed what we shall be, but when we see Him, we shall be like Him, for we shall see Him as He is".
6 For God, who commanded the light to shine out of darkness, hath shined in our hearts, to give the light of the knowledge of the glory of God in the face of Jesus Christ.
Our walk is by faith and not by sight, but we do have in sight one thing, ourselves. We can see in ourselves the difference God has made in our lives. The changes in how we think and feel and what is important, and how we act. And that change is seeing Jesus bringing His life into me. He has taken up residence, and is in the business of conforming us to be like Him, each of us in a way unique to each of us. Our true identity. Unknown until now, and not fully knowable until that day.
The more I see Him formed in me, the more this builds my faith to receive more of Him. Beholding as in a mirror the glory of the Lord, God's light shone into our hearts, and from our hearts, giving the light of knowing God's glory in the face of Jesus Christ. Our treasure, in earthen vessels. Jesus. Revealing Himself to us as He conforms our lives to be like His.
We don't see Him well, He's not yet formed. And we won't see the finished work until that day. But then, no more enigma!
It's an interesting discussion, and I can't say 1000% which way I see this, but the above is how it has me thinking.
Much love!