In that philosophical line from Hamlet, Ophelia is talking about transformation of the body, but it also applies to transformation of the mind and soul. Isn't this true for all of us, for all Christians? We know what we are now in so many ways. Medical science, biochemistry, kinesiology, psychology, and sociology - as well as poetry, art, music, and so on - tell us a lot about ourselves. They tell us about our bodies, our minds, and our souls. We know what we are, but we have no idea what we may be.
Science, psychology, philosophy, religion - none can tell us about the state of our souls. There is no way to measure or calculate out the ultimate choice that we've made, for good or evil, love or disobedience.
John writes a similar line--one I'm sure Shakespeare was familiar with--in his first letter:
What we know is that we are God's children. We know His promises for the future, and we can trust in them.See what love the Father has bestowed on us that we may be called the children of God. Yet so we are. The reason the world does not know us is that it did not know him. Beloved, we are God's children now; what we shall be has not yet been revealed. We do know that when it is revealed we shall be like him, for we shall see him as he is. (1 John 3:1-2)
Moreover, John tells us that "the word does not know us" because "it did not know him." For the world to know us--to really know who we are, not just as Christians but as humans--they must know Him. That goes for us as well. We're not exempt. We know ourselves better as we know Him better.