The promise of Gen 12:3, as well as the blessing of Gen 15:6, was given to Abraham BEFORE circumcision [Ro 4:9,10], and ultimately applies to the children of promise, NOT to the children of the flesh.
16 Now to Abraham were the promises spoken, and to his seed. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ.
17 Now this I say: A covenant confirmed beforehand by God, the law, which came four hundred and thirty years after, doth not disannul, so as to make the promise of none effect.
18 For if the inheritance is of the law, it is no more of promise: but God hath granted it to Abraham by promise.
19 What then is the law? It was added because of transgressions, till the seed should come to whom the promise hath been made; and it was ordained through angels by the hand of a mediator.
29 And if ye are Christ`s, then are ye Abraham`s seed, heirs according to promise. Gen 3
6.......For they are not all Israel, that are of Israel:
7 neither, because they are Abraham`s seed, are they all children: but, In Isaac shall thy seed be called.
8 That is, it is not the children of the flesh that are children of God; but the children of the promise are reckoned for a seed. Ro 9
And once again d-CON, there are no unfulfilled promises concerning Israel after the flesh:
43 So Jehovah gave unto Israel all the land which he sware to give unto their fathers; and they possessed it, and dwelt therein.
44 And Jehovah gave them rest round about, according to all that he sware unto their fathers: and there stood not a man of all their enemies before them; Jehovah delivered all their enemies into their hand.
45 There failed not aught of any good thing which Jehovah had spoken unto the house of Israel; all came to pass. Josh 21
And, behold, this day I am going the way of all the earth: and ye know in all your hearts and in all your souls, that not one thing hath failed of all the good things which Jehovah your God spake concerning you; all are come to pass unto you, not one thing hath failed thereof. Josh 23:14
Blessed be Jehovah, that hath given rest unto his people Israel, according to all that he promised: there hath not failed one word of all his good promise, which he promised by Moses his servant. 1 Ki 8:56
For how many soever be the promises of God, in him is the yea: wherefore also through him is the Amen, unto the glory of God through us. 2 Cor 1:20