"By faith, Abraham sojourned in the land of promise"--likewise, all those holy men and women of the Old Testament enumerated by St. Paul in his Epistle to the Hebrews, having endured many trials and tribulations and "having obtained a good report through faith, received not the promise...."
Today's Gospel records the geneology of Jesus Christ from Abraham: this shows, first of all, that Jesus, though fully divine, was at the same time fully human. And because He assumed all the fullness of our human nature, He was truly able to heal of of the effects of the ancestral sin. As the holy Fathers of the Church affirm, that which is not assumed cannot be healed. But it is also significant that these ancestors suffered and died in expectation of the promised Messiah.
They lived by faith, hoping "for a city which hath foundations, whose maker and builder is God." Truly, as the Holy Apostle affirms, "Faith is the substance of things hoped for." Nor is this the vague hope spoken of by certain politicians, who promise (but can never deliver) some sort of secular utopia.
This is rather a hope firmly rooted in God's promises, and thus worth suffering and dying for--as the holy martyrs throughout history bear witness. And while the Old Testament saints lived in expectation of the Messiah's coming, we live in expectation of His Second Coming, the Parousia, when He shall come to judge the living and the dead and to establish an eternal Kingdom that shall never pass away.
Through the Nativity of Christ, God fulfills the promise of His salvation, but we still await in hope the final consummation of the ages, when Christ shall be all in all. Let us, then, faithfully endure all things for the sake of Christ our Savior and His Kingdom, that having endured in hope, we may be found worthy of the promise.