Peter isn’t telling us to be happy. He says that if are reproached, defamed for the name of Christ, we will be happy.
On their part he is blasphemed, for the world reduces the most holy one to the lowest level that it possibly can. In his patience Christ allows this for a time, but only because he knows that all things will be corrected at the last day. The glory that he allows men to steal from him now is already restored in heaven, and will be restored through all creation at his return, when the Father shows how great is his anger that any should treat his Son in this way. Then the blasphemers will cover their faces and hide from his presence, realising that what they were allowed to steal, they must now be forced to pay back many times over. That sin which seemed so easy and was committed so thoughtlessly will fill them with horror as they see that they were all this time on God’s leash. They thought they were free to speak evil of their Creator, but God only waited with unfathomable patience to haul them in before his judgment seat to receive their sentence. But on our part he is glorified, for we treat him as he really is, the Lord of glory. We anticipate heaven’s revelation of his being and the universal acknowledgment of his exalted name. There cannot be a stronger contrast between the way heaven treats him and the way that a blaspheming world treats him. Christians observe with wonder the longsuffering of God. It pains them to see the world reproach him, but they know that this does not damage his glory, but only it enhances it, for it shows how much Christ is willing to suffer for the sake of his people.
The judgment of the world is passing away for it is a judgment of darkness, based on ignorance and prejudice against man’s Creator. It is a judgment that will not stand but which will in turn be judged. It is a very wonderful position to occupy, that we should be allowed to suffer for Christ’s sake by faithfully standing with him in the darkness of this world, when we know that very shortly, we will also stand with him in the full light of heaven. How pleased Christ will be with his people who were not ashamed of him under the withering gaze of human unbelief. It is a great blessing to have the Spirit of God resting upon us, but this is now the compensation of the Lord, even before the full light of day comes in the visible presence of the Lord Jesus Christ.