Considering how quickly our species tends to rush to revenge, these words from Joseph are incredible. Joseph's brothers had sold him into slavery, and they told his father he was dead. That really puts most of our problems into perspective. We've been short changed, robbed, cheated on, lied to, lied about, but we are fortunate in that this sort of thing just doesn't happen (much) anymore. You're not likely to be handed over to some randomly passing slave traders who drag you to a completely different country.
Furthermore, we know Joseph had the ability to exact revenge on his brothers. Because he was second only to Pharaoh, Joseph was able to arrest, enslave, even kill his brothers. We already saw him imprison them before he revealed his true identity to them. So he certainly had the legal authority to bring judgement upon them after Jacob was dead.
But Joseph bowed to a higher authority. He bowed to God. A God who commands forgiveness, and claims vengeance as His property. He also has the ability to use evil for good, and promises that for those who love Him and are called to His purpose, that will happen (Romans 8:28).
Just as Joseph forgave the unforgivable, so also should we forgive those who do us wrong. It is not our place to take revenge, as that belongs to God. Rather, let us forgive, and receive whatever good the Lord is willing to bring about because of the evil done against us.