And we rejoice in the hope of the glory of God. Not only so, but we also rejoice in our sufferings, because we know that suffering produces perseverance; perseverance, character; and character, hope. And hope does not disappoint us, because God has poured out his love into our hearts by the Holy Spirit, whom he has given us. Romans 5:2-5
We hope, not because we are not certain, but because we have a faith that transcends mere certainty. We hope, not because heaven is far away and we are stuck on earth, but because in the Incarnation, heaven was born in the form of a baby in Bethlehem, was crucified, died, and rose again.
We hope because the very worst thing that can possibly happen has already happened. There is no need to worry about anything leading to cosmic despair. Jesus has led the way to life from dead and has given us the gift of the Holy Spirit.
If God is for us, who can be against us? If God can bring eternal life for a race of murderers out of the death of his own murdered Son, what possible limits can there be to his mercy? None, except for our refusal to receive that mercy.