What is so important about Christian hope?
If our future is not secured and satisfied by God then we are going to be excessively anxious. This results either in paralyzing fear or in self-managed, greedy control. We end up thinking about ourselves, our future, our problems and our potential, and that keeps us from loving.
In other words, hope is the birthplace of Christian self-sacrificing love. That's because we just let God take care of us and aren't preoccupied with having to work to take care of ourselves. We say, "Lord, I just want to be there for other people tomorrow, because you're going to be there for me."
If we don't have the hope that Christ is for us then we will be engaged in self-preservation and self-enhancement. But if we let ourselves be taken care of by God for the future—whether five minutes or five centuries from now—then we can be free to love others. Then God's glory will shine more clearly, because that's how he becomes visible.
When God satisfies us so deeply that we're free to love other people then he becomes more manifest. And that's what we want above all.
What's the difference between a Christian definition of hope and the way it is usually used?
The word "hope" in ordinary English vocabulary is generally distinguished from certainty. We would say, "I don't know what's going to happen, but I hope it happens."
When you read the word "hope" in the Bible (like in 1 Peter 1:13—"set your hope fully on the grace that will be brought to you at the revelation of Jesus Christ"), hope is not wishful thinking. It's not "I don't know if it's going to happen, but I hope it happens." That's absolutely not what is meant by Christian hope.
Christian hope is when God has promised that something is going to happen and you put your trust in that promise. Christian hope is a confidence that something will come to pass because God has promised it will come to pass.
How do we build our hope in God?
Hope is a portion or part of faith. Faith and hope, in my mind, are overlapping realities: hope is faith in the future tense. So most of faith is hope.
The Bible says, "Faith comes by hearing and hearing by the word of God" (Romans 10:17). This implies that hope, like faith, is also strengthened by the word of God. Hope comes from reading his precious and very great promises and looking to Christ who purchased them.
I would sum it up like this: The most important verse in the Bible for me, probably, is Romans 8:32:
He who did not spare his own Son but gave him up for us all, how will he not also with him graciously give us all things?
Now that last part is hope producing! But it's grounded in the rock-solid statement that "God didn't spare his own son."
So the essence of what we look to in the Bible to build our hope is, What has Christ done for me in my sinful condition that enables me to know that I will not come in to judgment and condemnation and that all things are working together for my good? And the answer is that Christ died for me, rose again for me, and therefore all the promises of God are yes in him.
So let's look away from the circumstances that confront us, look to Christ, look to the promises, and hold fast to them. Hope comes from the promises of God rooted in the work of Christ.