The adoption of a more optimistic outlook among modern Amillennialists with regard to the Gospel is not without biblical foundation. Postmillennialists have long held that the Gospel of Jesus Christ would eventually hold sway in the world. Indeed, it is a guarantee in the New Covenant.
"But this is the covenant that I will make with the house of Israel after those days, declares the LORD: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people. And no longer shall each one teach his neighbor and each his brother, saying, 'Know the LORD,' for they shall all know me, from the least of them to the greatest, declares the LORD. For I will forgive their iniquity, and I will remember their sin no more." (Jeremiah 31:33-34)
Considering the following passages, many of which concern the outgrowth of the First Advent of Christ, being completely absent of an earthly millennium.
"But truly, as I live, and as all the earth shall be filled with the glory of the LORD,"
"As for me, I have set my King on Zion, my holy hill. I will tell of the decree: The LORD said to me, "You are my Son; today I have begotten you. Ask of me, and I will make the nations your heritage, and the ends of the earth your possession. You shall break them with a rod of iron and dash them in pieces like a potter's vessel."
"All the ends of the earth shall remember and turn to the LORD, and all the families of the nations shall worship before you. For kingship belongs to the LORD, and he rules over the nations."
"May he have dominion from sea to sea, and from the River to the ends of the earth! May desert tribes bow down before him and his enemies lick the dust! May the kings of Tarshish and of the coastlands render him tribute; may the kings of Sheba and Seba bring gifts! May all kings fall down before him, all nations serve him!"
"Nations will fear the name of the LORD, and all the kings of the earth will fear your glory."
"A Psalm of David. The LORD says to my Lord: "Sit at my right hand, until I make your enemies your footstool.""
"All the kings of the earth shall give you thanks, O LORD, for they have heard the words of your mouth, and they shall sing of the ways of the LORD, for great is the glory of the LORD."
"It shall come to pass in the latter days that the mountain of the house of the LORD shall be established as the highest of the mountains, and shall be lifted up above the hills; and all the nations shall flow to it, and many peoples shall come, and say: "Come, let us go up to the mountain of the LORD, to the house of the God of Jacob, that he may teach us his ways and that we may walk in his paths." For out of Zion shall go the law, and the word of the LORD from Jerusalem. He shall judge between the nations, and shall decide disputes for many peoples; and they shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war anymore."
"For to us a child is born, to us a son is given; and the government shall be upon his shoulder, and his name shall be called Wonderful Counselor, Mighty God, Everlasting Father, Prince of Peace. Of the increase of his government and of peace there will be no end, on the throne of David and over his kingdom, to establish it and to uphold it with justice and with righteousness from this time forth and forevermore. The zeal of the LORD of hosts will do this."
"The wolf shall dwell with the lamb, and the leopard shall lie down with the young goat, and the calf and the lion and the fattened calf together; and a little child shall lead them. The cow and the bear shall graze; their young shall lie down together; and the lion shall eat straw like the ox. The nursing child shall play over the hole of the cobra, and the weaned child shall put his `hand on the adder's den. They shall not hurt or destroy in all my holy mountain; for the earth shall be full of the knowledge of the LORD as the waters cover the sea. In that day the root of Jesse, who shall stand as a signal for the peoples--of him shall the nations inquire, and his resting place shall be glorious."
"Turn to me and be saved, all the ends of the earth! For I am God, and there is no other. By myself I have sworn; from my mouth has gone out in righteousness a word that shall not return: To me every knee shall bow, every tongue shall swear allegiance. Only in the LORD, it shall be said of me, are righteousness and strength; to him shall come and be ashamed all who were incensed against him. In the LORD all the offspring of Israel shall be justified and shall glory."
"For the earth will be filled with the knowledge of the glory of the LORD as the waters cover the sea."
"On that day living waters shall flow out from Jerusalem, half of them to the eastern sea and half of them to the western sea. It shall continue in summer as in winter. And the LORD will be king over all the earth. On that day the LORD will be one and his name one."
1 Corinthians 15:24-26
"Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power. For he must reign until he has put all his enemies under his feet. The last enemy to be destroyed is death."
Amillennialists have a tendency to "spiritualize" these texts as being symbolic of the church age. Postmillennialists hold that these promises are guaranteed in the Great Commission, where Christ commands us to “make disciples of all nations” and promises to be with us until the end of the age.