Wouldn't the figure between Isaac and Ishmael be shown between (those who are Abraham's seed, in Christ) and the that which is of the law?
For example,
Gal 4:29 But as then he that was born after the flesh (Ishmael) persecuted him (Isaac) that was born after the Spirit, even so it is now.
Which thing is shown us in Ishmael, which is according to the law as Paul points out whene he says
Gal 4:21 Tell me, ye that desire to be under the law, do ye not hear the law?
Which would be found allegorically in one of Abraham's sons (Ishmael)
Gal 4:22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
The children of the promise is in accordance with Isaac (the son of the free) as Paul said here
Gal 4:28 Now we, brethren, as Isaac was, are the children of promise
Whereas he says, Hagar answereth to Jerusalem (the bondwoman) which now is, who persecutes and kills the prophets
Jesus aknowledges the same as the seed of Abraham (according to the flesh) when he said,
John 8:37 I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you.
Abraham's seed, or children (according to the flesh)
1 Thes 2:15 Who both killed the Lord Jesus, and their own prophets, and have persecuted us; and they please not God, and are contrary to all men
The same were said to be of the law according Paul's allegory
Gal 3:12 And the law is not of faith: but, The man that doeth them shall live in them.
Also considered a nation (in the singular sense)
Gen 21:13 And also of the son of the bondwoman will I make a nation, because he is thy seed.
Children of the prophets (as Abraham was a prophet) to whom the promise was made, which was to Abraham, and His seed, which is Christ
Acts 3:25 Ye are the children of the prophets, and of the covenant which God made with our fathers, saying unto Abraham, And in thy seed shall all the kindreds of the earth be blessed.
Through Christ, whom as concerning the flesh Christ came
Romans 9:5 Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever. Amen.
Acts 3:26 Unto you first God, having raised up his Son Jesus, sent him to bless you, in turning away every one of you from his iniquities.
Their rejection
Luke 13:35 Behold, your house is left unto you desolate: and verily I say unto you, Ye shall not see me, until the time come when ye shall say, "Blessed is he that cometh in the name of the Lord."
Then ofcourse they who he would send
Mat 10:40 He that receiveth you receiveth me, and he that receiveth me receiveth him that sent me.
These are called his brethren
Heb 2:11 For both he that sanctifieth and they who are sanctified are all of one: for which cause he is not ashamed to call them brethren
After he was lifted up (crucified) at his rising they would preach Christ to all nations (Psalm 2:8)
We (of the nations, whether Jew or Gentile, who are not a people) are made accepted in the beloved (in Jesus Christ, His beloved Son)
Romans 9:25 As he saith also in Osee, I will call them my people, which were not my people; and her beloved, which was not beloved.
Which is inclusive of both those who are called of the Jews and of the Gentiles by his grace
Romans 9:24 Even us, whom he hath called, not of the Jews only, but also of the Gentiles?
Am I missing something?