I've read the thread .... sorry to be late coming in.
Jesus explained what "seed" is:
Mat. 13:18 “Therefore hear the parable of the sower: 19 When anyone hears the word of the kingdom, and does not understand it, then the wicked one comes and snatches away what was sown in his heart. This is he who received seed by the wayside.20 But he who received the seed on stony places, this is he who hears the word and immediately receives it with joy; 21 yet he has no root in himself, but endures only for a while. For when tribulation or persecution arises because of the word, immediately he stumbles. 22 Now he who received seed among the thorns is he who hears the word, and the cares of this world and the deceitfulness of riches choke the word, and he becomes unfruitful. 23 But he who received seed on the good ground is he who hears the word and understands it, who indeed bears fruit and produces: some a hundredfold, some sixty, some thirty.”
See also Jesus' reason for teaching in parables - Mat. 13:10-16
Why did Jesus declare that Zacchaeus was a child of Abraham? Luke 19:1-10
9 And Jesus said to him, “Today salvation has come to this house, because he also is a son of Abraham; 10 for the Son of Man has come to seek and to save that which was lost.”
NOT by his DNA, but he heard the word of Jesus, repented, & showed his repentance by his changed life.
Being a Jew does not make a person a born again child of God, as John explained:
John 1:10 He was in the world, and the world was made through Him, and the world did not know Him. 11 He came to His own, and His own did not receive Him. 12 But as many as received Him, to them He gave the right to become children of God, to those who believe in His name: 13 who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
A Biblical covenant is essentially the promise of God, a promise of blessing usually on condition of obedience.
The "rainbow covenant" is an exception - a declaration of God providential care for the earth & is unconditional.
We can NEVER fulfill the condition of perfect obedience - that's where Jesus, THE Seed of Abraham comes in on our behalf.
God's first promise to Abram is in fact a covenant:
Gen. 12:2 I will make you a great nation;
I will bless you
And make your name great;
And you shall be a blessing.
3 I will bless those who bless you,
And I will curse him who curses you;
And in you all the families of the earth shall be blessed.”
Restatements of that covenant promise make it clear that it is through the seed of Abraham that that promise will be realised, and the New Covenant writers explain that "seed" is singular, referring to the LORD Jesus Christ.
Certainly Abraham's descendants became a great nation (what is the Hebrew word used for "nation"?) & Joshua & Solomon acknowledge that fact. That aspect of the promise was fulfilled. They did possess the promised land. But was that promised land on earth what Abraham & the Patriarchs hoped for?
Heb. 11: 9 By faith he dwelt in the land of promise as in a foreign country, dwelling in tents with Isaac and Jacob, the heirs with him of the same promise; 10 for he waited for the city which has foundations, whose builder and maker is God.
.....
13 These all died in faith, not having received the promises, but having seen them afar off were assured of them, embraced them and confessed that they were strangers and pilgrims on the earth. 14 For those who say such things declare plainly that they seek a homeland. 15 And truly if they had called to mind that country from which they had come out, they would have had opportunity to return. 16 But now they desire a better, that is, a heavenly country. Therefore God is not ashamed to be called their God, for He has prepared a city for them.
The NH&NE is the ultimate promised land.
But only
in Christ & the Gospel of salvation are all families, all nations blessed. That, of course, includes the Jews, whether or not they have the right DNA. Vast numbers responded to the preaching of John, & followed Jesus as directed by John. At Pentecost, 3,000 Jews from every nation responded, & 5,000 a few days later, then priests, then many thousands.
The idea that God has shut out his chosen people, the apple of his eye, for over 50 generations is repugnant. The Gospel of repentance & faith in Jesus Christ, God & Saviour, is open to all.
Many thousands of Jews believed and formed the church.
Acts 2:46 So continuing daily with one accord in the temple, and breaking bread from house to house, they ate their food with gladness and simplicity of heart, 47 praising God and having favor with all the people. And the Lord added to the church daily those who were being saved.
Believing Jews took Jesus' warning & fled Jerusalem before the destruction of the city & of those who continued in rejection of their Messiah. They had learnt that now believing Gentiles were one body with them as the people of God, so there was no need to keep separate.
We have the New - Everlasting - Covenant in the blood of Jesus:
Heb. 13:20 Now may the God of peace who brought up our Lord Jesus from the dead, that great Shepherd of the sheep, through the blood of the everlasting covenant, 21 make you complete in every good work to do His will, working in you what is well pleasing in His sight, through Jesus Christ, to whom be glory forever and ever. Amen.
But, is the modern Israel the fulfilment of OT prophecy? I think not - the state is built by those who reject Jesus & his Gospel, and who also reject the Law of Moses, & the teaching of the OT Prophets.