Three days before Jesus was put to death, after having scathingly condemned the Pharisees, Jesus said concerning the nation of fleshly Israel: "Jerusalem, Jerusalem, the killer of the prophets and stoner of those sent forth to her,—how often I wanted to gather your children together, the way a hen gathers her chicks together under her wings! But you people did not want it. Look! Your house (the temple in Jerusalem) is abandoned ("abandoned", Greek eremos, meaning "solitary, lonely, desolate, uninhabited, deserted by others, deprived of the aid and protection of others, esp. of friends, acquaintances, kindred; bereft", Thayer's Greek-English Lexicon of the New Testament, pg 249) to you. For I say to you, you will by no means see me from now until you say, ‘Blessed is he that comes in Jehovah’s name!’” (Matt 23:37-39, with Jesus quoting from Ps 118:26)
Thus, the nation of fleshly Israel, with their temple in Jerusalem, was "abandoned" by God. Why ? Because they as a nation was "the killer of the prophets and stoner of those sent forth to her", with the central governing body of religious leaders in Jerusalem having Jesus killed at the hands of the Romans.(1 Thess 2:14, 15)
As a nation, fleshly Israel is no longer God's people, having been replaced by another "nation". On the same day as when Jesus raked the Jewish religious leaders "over the coals", he also said to them: "Did you never read in the Scriptures (at Isa 28:16), ' The stone that the builders rejected, this has become the chief cornerstone. This has come from Jehovah, and it is marvelous in our eyes ? Thus is why I say to you (the Jewish religious who represented the nation of fleshly Israel), the kingdom of God will be taken from you (given the opportunity to be "the kingdom of God" to fleshly Israel on Mt Sinai in 1513 B.C.E., Ex 19:5, 6) and be given to a nation producing its fruits."(Matt 21:42, 43)
Hence, at Revelation 7, the 144,000 "sealed out of every tribe of the sons of Israel" are not the nation of fleshly Israel, but rather those selected by God who are "producing its (God's kingdom) fruits". What are the "fruits" that this new "nation" would produce ? Galatians 5 provides the nine "fruitage of the (God's) spirit", as "love, joy, peace, patience, kindness, goodness, faith, mildness, self-control."(Gal 5:22, 23)
Rather than having showed these necessary spiritual qualities, the nation of fleshly Israel have continued to display a murderous spirit, despite Jesus having "fertilized" the nation with "the good news of the Kingdom of God" (Luke 8:1) for some 3 1/2 years, from 29 to 33 C.E.(Luke 13:6-9)
That is also why the apostle Paul wrote to the Romans: "For not all who descend from Israel are really "Israel". Neither are they all God's children because they are Abraham's offspring....That is, the children in the flesh (fleshly Israel) are not really the children of God."(Rom 9:6-8)
Since the "children in the flesh", or fleshly Israel, are not "the children of God", then who is ? Paul says that "all those who walk orderly (displaying the "fruitage of the spirit") by this rule of conduct, peace and mercy be upon them, yes, upon the Israel of God."(Gal 6:16) The "kingdom of God" has now shifted from fleshly Israel to spiritual Israel, the "nation producing its fruits (of God's kingdom)".
These are the ones who have followed in Jesus "footsteps", so that "when he was being insulted, he did not insult in return. When he was suffering, he did not threaten, but he entrusted himself to the One (Jehovah God) who judges righteously."(1 Pet 2:21, 23) These are the ones who have ' beaten their swords into plowshares and spears into pruning shears...nor will they learn war anymore.' (Isa 2:4)