These two verses are common proof-texts used by Amillennialists who make the false assumption that the “heavenly” new Jerusalem must be understood as nonearthly. Amillennialism frequently makes this false dichotomy, and you need to be aware of this in order to respond properly and Biblically.
The following is an excerpt from Robert L. Saucy’s book, The Case For Progressive Dispensationalism. pp. 53-57. (By the way, Part 4 of his book is priceless for those who are interested in solid, scholarly arguments for the Premillennial position.)
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Finally, in relation to the land promise, there is the teaching of the writer to the Hebrews concerning the hoped for destination of Abraham and the patriarchs. Of Abraham, it is said, “. . . he was looking forward to the city with foundations, whose architect and builder is God” (Heb 11:10). Likewise, the patriarchs, as “aliens and strangers on earth, . . . were longing for a better country–a heavenly one” (11:13, 16). The divine construction of the city and the heavenly nature of the country lead many scholars to understand the goal of Abraham and the other patriarchs as heaven rather than any earthly land of the Old Testament promises. For example, F. F. Bruce states,

The truth is, their true homeland was not on earth at all. The better country on which they had set their hearts was the heavenly country. The earthly Canaan and the earthly Jerusalem were but temporary object-lessons pointing to the saint’s everlasting rest, the well-founded city of God [The Epistle to the Hebrews, 305].

There is no question that the writer’s description of their hope involved something more than the land of Canaan of their day. But a simple dichotomy between earthly Jerusalem and Canaan on the one hand and heaven on the other, with the implication that the literal land promise of the Abrahamic hope has been transcended in the New Testament, does not seem justified in light of the total biblical evidence.
In the first place, we should note that the immediate context refers to the literal land of Canaan, where Abraham lived “like a stranger,” as “the promised land” (Heb 11:9). Isaac and Jacob are described as “heirs with him of the same promise,” which can only be a reference to the same “promise land.” These statements surely bear some relation to the many Old Testament promises of the land given to the patriarchs. In addition, the hoped-for destination of “a country of their own” is not contrasted to earthly Canaan, but to “the country they had left,” namely, Mesopotamia. Thus it seems that we should not understand the promised destination as altogether separate from the earthly land promised in the Old Testament.
However, the language clearly portrays a situation beyond the temporal and beyond the transitory nature of the land in which Abraham and his descendants lived. The question is, was this eternal dimension somehow an aspect of the promise? Did the patriarch’s hope included a final, incorruptible heavenly city and country? The answers to these questions are already suggested in the Old Testament pictures of the new Jerusalem and a new earth.
As the “city of God” where he revealed his presence, the historical Jerusalem was already seen as founded by God. Thus the psalmist declared that God “built his sanctuary . . . like the earth that he established forever” (Ps 78:69). God himself “set his foundation [of Zion] on the holy mountain” (Ps 87:1; cf. Isa 14:32). But the prophets looked also to a renewed Jerusalem in the future. After the divine judgment that was to come on Jerusalem because of apostasy, God would return to bring salvation to the city (Isa 49:14f.; 41:27; 46:13; Zep 3:16-17). Into a darkness reminiscent of the first day of creation, God’s light would arise to shine on Zion (Isa 60:1-2).
In the Old Testament the new, eschatological Jerusalem to be created by God’s saving and redeeming action is pictured as an earthly city. But, as Georg Fohrer puts it, these predictions become “the starting point for the later idea of an upper or heavenly Jerusalem.” Of the “many and varied” explanations of the Jerusalem of the last days found in the apocalyptic writings, Eduard Lohse says,

On the one hand Jerusalem at the end of the days is the city of David built again with glory and magnificence. On the other the new Jerusalem is thought of as a pre-existent city which is built by God in heaven and which comes down to earth with the dawn of a new world.

Yet the description of the new Jerusalem as “heavenly” must not be hastily understood as nonearthly. When Jesus and the disciples announced the nearness of the “kingdom of heaven” (cf. Mt 4:17), they were not referring to a nonearthly entity. Rather, they were proclaiming the coming of the reign of God on the earth (cf. Mt 6:10: “Your kingdom come, your will be done on earth…”). The writer of Hebrews already gave a clue to his meaning of “heaven” in speaking of those “who share in the heavenly calling” (Heb 3:1) and “who have tasted the heavenly gift” (6:4). These phrases describe those who are participating in divine realities that have their origin from God in heaven, but who are locally on earth.
To describe Jerusalem and the country as heavenly is simply to speak of them in their final eternal state, which is the result of God’s salvation. The hope of the patriarchs and the prophets for a restored earthly Jerusalem ultimately merged into a Jerusalem of eternal, heavenly quality created anew by the final salvation of God. The final goal of such as “heavenly” land, however, does not negate the prophecies of a historical restoration of the nation of Israel to the land before that final regenerative action. Admittedly, the specific nature of the final “heavenly” fulfillment and its relation to the historical promised land is not clear. Perhaps the extension of the land promise of the Old Testament in to an inheritance of the earth may be paradigmatic of a general universalization of God’s blessing in the final state.
The blending by the prophets of a future restored Jerusalem and the final eternal city corresponds with their picture of the future of the entire earth and heavens. The hope of the Old Testament was ultimately for an eternal state of things, for the prophets knew that the present “heavens will vanish like smoke, the earth will wear out like a garment” (Isa 51:6). Consequently, along with their portrayal of the rule of the Messiah over a yet imperfect world (cf. Isa 2:1-4; Zec 14:16ff.), they looked forward to the creation of “new heavens and a new earth” (Isa 65:17; 66:22).
[Footnotes: (44) The belief in a temporary kingdom of the Messiah before the final perfect Age to Come was prevalent in the Jewish apocalyptic writings, cf. D. S. Russell, The Method and Message of Jewish Apocalyptic (Philadelphia: Westminster, 1964), 291-97. (45) It is noteworthy that contexts even of the statements concerning the new heavens and earth contain references that can only refer to the yet imperfect state before eternity (cf. Isa 65:20-23). Thus th Old Testament prophetic picture does not draw as clear a line of chronological demarcation between the present history and the final perfect state as appears in Revelation 20-22.]
Even as these references to the final perfected “new heavens” and “new earth” did not cancel out the historical prophecies that were to come before the end, so the references to the final country and Jerusalem in the book of Hebrews do not negate the reality of the historical before their ultimate arrival. The writer to the Hebrews speaks of believers as already having come to the heavenly Jerusalem (Heb 12:22), but this does not negate the reality of the present earthly history of the church that is not existentially lived in the new Jerusalem. Similarly, it need not negate the reality of a future period in which the historical earthly promises about Jerusalem and the land are fulfilled in further preparation for the eternal realities.
[Footnote: (46) . . . . As illustration of the Jewish understanding of the relationship between the earthly and the heavenly is seen in the statement by Rabbi Yohanan in the third century. In contrast to Origen, he refused to separate the earthly and heavenly cities: “The Holy One . . . said: I will not enter the Jerusalem which is above until I enter the Jerusalem which is below”. . .]
In this connection it is important to recognize that the purpose of the writer to the Hebrews is not to give us an interpretation of Old Testament prophecy. The book is rather a “word of exhortation” (13:22), which Bruce describes as a “form of sermon or homily.” Using material not from the prophets but primarily from the Psalms, with other materials added to elaborate the argument, the writer’s goal was to establish the superiority of the gospel in contrast to all that went before, particularly the levitical system. The primary evidence of the supremacy of Christianity is presented in its finality. Coming to Christ means final access to God without any barrier.
The writer’s references to heavenly realities must be understood in the context of this teaching of finality. Even as Paul’s teaching of present access to God does not do away with the actual historical situation of the church (cf. Eph 2:18). so our present coming to the heavenly Jerusalem must not be seen to deny the historical reality of prophecy. Abraham’s hope for eternal realities, likewise, does not negate the reality of the history that, according to God’s prophecy, must intervene before the actual attaining of the perfect state.
Thus the land aspect of the Abrahamic promise retains validity in the New Testament. Its link to the nation of Israel and to the coming kingdom indicates that the fulfillment of the land promise awaits the future both in this earth and in the new “heavenly” earth to come. There is no evidence that the promise of the land has been either completely fulfilled historically or reinterpreted to mean a symbol of heaven or the blessing of spiritual life in general.