The doctrine of Biblical replacement theology in a nut shell, teaches that all the OLD TESTAMENT promises given to Israel are forfeited and given to the Church because they rejected their Messiah.
Basically, yes.
The Old Covenant was based on the performance of the people. Do this and be blessed. Don't do it and be cursed.
That covenant is over. There is a New Covenant now. A Better Covenant. One that is not based on the performance of people but the performance of God.
Galatians 3:28-29
28 There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
29 And if ye be Christ's, then are ye Abraham's seed,
and heirs according to the promise.
Romans 9:6-8
6 Not as though the word of God hath taken none effect. For they are not all Israel, which are of Israel:
7 Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called.
8 That is,
They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed.
Hebrews 7:19-22
19 For the law made nothing perfect, but the bringing in of a better hope did; by the which we draw nigh unto God.
20 And inasmuch as not without an oath he was made priest:
21 (For those priests were made without an oath; but this with an oath by him that said unto him, The Lord sware and will not repent, Thou art a priest for ever after the order of Melchisedec
22 By so much was Jesus made a surety of a better testament.
Hebrews 8:7-9
7 For if that first covenant had been faultless, then should no place have been sought for the second.
8 For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant with the house of Israel and with the house of Judah:
9 Not according to the covenant that I made with their fathers in the day when I took them by the hand to lead them out of the land of Egypt; because they continued not in my covenant, and I regarded them not, saith the Lord.
Isaiah 28:16-18
16 Therefore thus saith the Lord God, Behold, I lay in Zion for a foundation a stone, a tried stone, a precious corner stone, a sure foundation: he that believeth shall not make haste.
17 Judgment also will I lay to the line, and righteousness to the plummet: and the hail shall sweep away the refuge of lies, and the waters shall overflow the hiding place.
18 And
your covenant with death shall be disannulled, and your agreement with hell shall not stand; when the overflowing scourge shall pass through, then ye shall be trodden down by it.
Its not impossible for the children of the flesh to be a part of the New Covenant. It is not impossible for them to be Heirs according to the Promise. It is not impossible for them to be the Children of God, Gods People.
All they have to do is come to Christ. Humble themselves and ask.