Jesus will come again, but he is the perfect that came the first time.
1 Corinthians 13:11 When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.
When we were children is about being under the old law.
Galatians 3:24 So the law was our guardian until Christ came that we might be justified by faith.
So now that Jesus has come, we are no longer as a child. The perfect has come.
We no longer see through a glass darkly, for they have seen him face to face.
12 For now we see through a glass, darkly; but then face to face: now I know in part; but then shall I know even as also I am known.
13 And now abideth faith, hope, charity, these three; but the greatest of these is charity
The Old Testament believers waited a long time for God to reveal Jesus to us, and in the New Testament time people prophesied about what God finally revealed to us what He wanted us to know. We have the mysteries revealed, and we have all the teachings we need to lead us to eternal life, we cannot add or subtract from the finished work, we cannot add new prophecies and knowledge to the Bible. The perfect has come.
When you only have prophesy in part (as in the Old Testament times), the prophecy has not yet been fulfilled, and more prophecy is needed, it is imperfect. However, when there is fulfillment of prophecy (as in the New Testament times), then we have full understanding; so then, it is perfect and, that which is perfect is come.