When I tell people I have a medal from a half marathon, they tend not to believe that I acquired it through completion of that event -- correctly as it turns out, since it was given to me as a gift. Possibly it was meant to inspire me, in which case it has yet to succeed, but you can see how completing a marathon, or more precisely a half marathon, might be good for me, even if difficult to achieve.
When we think about hope, we tend to have in mind either a sense of general confidence in the future or some more focused sense directed at particular desires. In this more focused sense, we desire a good that is difficult to attain, regardless of whether that good is attainable through our own efforts or not.
This type of hope is characterised both by what it is that we hope for and the means by which our hope is to be fulfilled. And whilst typically when one hopes in this sense, one has a good idea about both of these, nevertheless this is not always so. Hence such hopes can vary according to whether one or both of these elements are met and according to how good one's idea is about one or both of these elements.
Thus in the case of my half marathon, were I to hope to complete it, what it is that I am hoping for is fairly clear, as is the means of fulfilling that hope; train hard. Christian hope, however, is slightly and importantly different from this. Whilst we know that we hope for the beatific vision, we do not have a good idea about its content. And it is this lack of certitude which the Gospel exploits in challenging our assumptions about Christian hope.
The occasion for the challenge is when the Sadducees try to show that the Mosaic Law and Christ's preaching are incompatible because the former cannot allow for resurrection whilst the latter requires it. However, if we are to enjoy the beatific vision after death then we must rise from the dead, but if we do not rise from the dead we cannot enjoy the beatific vision after death. Hence if the Sadducees' objection is correct, Christian hope for the beatific vision will be false.
Of course this is not the case, and Christ's reply shows that the Sadducees have misunderstood the resurrection and hence what the object of Christian hope is. Since resurrected life is a new departure for human life, a life without death, it will be different from the life we experience now.
So whilst people marry in this life, in the next they will not, thus there can be no contradiction derived from an account of marriage in this life and applied to the situation which obtains in the next. The Sadducees' objection fails then: resurrection is not made impossible and our hope for the beatific vision is not affected.
But where does this leave marriage? Marital love is special and particular, particular to spouses and consequently exclusive of others. In the beatific vision, however, one loves all people just as God loves them, by sharing God's very love for people in a way that excludes no one. In effect marital love is extended and perfected, so that what's best about human beings in this life is made available in an even better way to all of us in the next life.
As for our hope, during this life such knowledge as we have of its object is only acquired through accepting Christ's revelation in faith. But just as in possession of the beatific vision one's love extends to all, so also when one's hope for the beatific vision is infused by charity, that hope is extended to desiring that vision for all people.
So through Christ's instruction we come to hope that the beatific vision, which will be perfective of ourselves, will also be perfective of other people. In effect, we come to desire for others what we desire for ourselves and thus experience in this life a foretaste of the life to come.