6 Ah! How great a dignity! He vouch-safed “to be called their God.” What do you say? He is called the God of the earth, and the God of Heaven, and have you set it down as a great thing that “He is not ashamed to be called their God”? Great and truly great this is, and a proof of exceeding blessedness. How? Because He is called God of earth and of heaven as also of the Gentiles: in that He created and formed them: but [God] of those holy men, not in this sense, but as some true friend.
And I will make it plain to you by an example; as in the case of [slaves] in large households, when any of those placed over the household are very highly esteemed, and manage everything themselves, and can use great freedom towards their masters, the Master is called after them, and one may find many so called. But what do I say? As we might say the God, not of the Gentiles but of the world, so we might say “the God of Abraham.” But you do not know how great a dignity this is, because we do not attain to it. For as now He is called the Lord of all Christians, and yet the name goes beyond our deserts: consider the greatness if He were called the God of one [person]! He who is called the God of the whole world is “not ashamed to be called” the God of three men: and with good reason: for the saints would turn the scale, I do not say against the world but against ten thousand such. “For one man who does the will of the Lord, is better than ten thousand transgressors.”
Now that they called themselves “strangers” in this sense is manifest. But supposing that they said they were “strangers” on account of the strange land, why did David also [call himself a stranger]? Was not he a king? Was not he a prophet? Did he not spend his life in his own country? Why then does he say, “I am a stranger and a sojourner”? How are you a stranger? “As” (he says) “all my fathers were.” Do you see that they too were strangers? We have a country, he means, but not really our country. But how art you yourself a stranger? As to the earth. Therefore they also [were strangers] in respect of the earth: For “as they were,” he says, so also am I; and as he, so they too.
Source: Homilies on the Epistle to the Hebrews (New Advent)