The Covenant With Abraham's Seed
While Abraham was still childless, the LORD made a covenant with Abraham regarding his children:
"15:1 After these things the word of the LORD came unto Abram in a vision, saying, Fear not, Abram: I am thy shield, and thy exceeding great reward.
15:2 And Abram said, Lord GOD, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus? 15:3 And Abram said, Behold, to me thou hast given no seed: and, lo, one born in my house is mine heir.
15:4 And, behold, the word of the LORD came unto him, saying, This shall not be thine heir; but he that shall come forth out of thine own bowels shall be thine heir. 15:5 And he brought him forth abroad, and said, Look now toward heaven, and tell the stars, if thou be able to number them: and he said unto him, So shall thy seed be.
15:6 And he believed in the LORD; and he counted it to him for righteousness." (Genesis 15:1-6 KJV)
"Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I AM"
Abraham was also a prophet, given to know about the Exodus of his descendants, long before any of them were born (see also The Exodus Prophecy).
"15:13 And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land that is not theirs, and shall serve them; and they shall afflict them four hundred years;
15:14 And also that nation, whom they shall serve, will I judge: and afterward shall they come out with great substance. 15:15 And thou shalt go to thy fathers in peace; thou shalt be buried in a good old age. 15:16 But in the fourth generation they shall come hither again: for the iniquity of the Amorites is not yet full." (Genesis 15:13-16 KJV)
"15:18 In the same day the LORD made a covenant with Abram, saying, Unto thy seed have I given this land, from the river of Egypt unto the great river, the river Euphrates: 15:19 The Kenites, and the Kenizzites, and the Kadmonites, 15:20 And the Hittites, and the Perizzites, and the Rephaims, 15:21 And the Amorites, and the Canaanites, and the Girgashites, and the Jebusites." (Genesis 15:18-21 KJV)
The Messianic line from Abraham (keeping in mind that it was Jesus Christ Himself who brought it about - see 'Before Abraham Was, I AM' to understand that the "God of the Old Testament" was "the LORD God" who was born as Jesus Christ) through the miraculous birth of Isaac ("17:17 Then Abraham fell upon his face, and laughed, and said in his heart, Shall a child be born unto him that is an hundred years old? and shall Sarah, that is ninety years old, bear?" Genesis 17:17 KJV), numerous other children were born to Abraham through a number of wives and concubines.
"16:15 And Hagar bare Abram a son: and Abram called his son's name, which Hagar bare, Ishmael.
16:16 And Abram was fourscore and six years old, when Hagar bare Ishmael to Abram." (Genesis 16:15-16 KJV)
"21:1 And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken.
21:2 For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him. 21:3 And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac." (Genesis 21:1-3 KJV)
"25:1 Then again Abraham took a wife, and her name was Keturah. 25:2 And she bare him Zimran, and Jokshan, and Medan, and Midian, and Ishbak, and Shuah. 25:3 And Jokshan begat Sheba, and Dedan. And the sons of Dedan were Asshurim, and Letushim, and Leummim. 25:4 And the sons of Midian; Ephah, and Epher, and Hanoch, and Abidah, and Eldaah. All these were the children of Keturah." (Genesis 25:1-4 KJV)
As plainly stated in the Scriptures quoted above, the Messianic line went through Isaac - and the physical Israelites in general. But there is only one Messiah. And what about the descendants of Abraham's other children - and of humanity in general? Are they all left out of the blessings that were promised to "Abraham's seed"? No, they are not. We know that from the Word of the Messiah Himself who explained just who "Abraham's seed" ultimately are - and that it was the Messiah Himself Who declared it right in the time of Abraham.
"8:31 Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed; 8:32 And ye shall know the truth, and the truth shall make you free.
8:33 They answered him, We be Abraham's seed, and were never in bondage to any man: how sayest thou, Ye shall be made free?
8:34 Jesus answered them, Verily, verily, I say unto you, Whosoever committeth sin is the servant of sin. 8:35 And the servant abideth not in the house for ever: but the Son abideth ever. 8:36 If the Son therefore shall make you free, ye shall be free indeed. 8:37 I know that ye are Abraham's seed; but ye seek to kill me, because my word hath no place in you.
8:38 I speak that which I have seen with my Father: and ye do that which ye have seen with your father.
8:39 They answered and said unto him, Abraham is our father.
Jesus saith unto them, If ye were Abraham's children, ye would do the works of Abraham. 8:40 But now ye seek to kill me, a man that hath told you the truth, which I have heard of God: this did not Abraham. 8:41 Ye do the deeds of your father.
Then said they to him, We be not born of fornication; we have one Father, even God.
8:42 Jesus said unto them, If God were your Father, ye would love me: for I proceeded forth and came from God; neither came I of myself, but he sent me. 8:43 Why do ye not understand my speech? even because ye cannot hear my word. 8:44 Ye are of your father the devil, and the lusts of your father ye will do. He was a murderer from the beginning, and abode not in the truth, because there is no truth in him. When he speaketh a lie, he speaketh of his own: for he is a liar, and the father of it. 8:45 And because I tell you the truth, ye believe me not.
8:46 Which of you convinceth me of sin? And if I say the truth, why do ye not believe me?
8:47 He that is of God heareth God's words: ye therefore hear them not, because ye are not of God.
8:48 Then answered the Jews, and said unto him, Say we not well that thou art a Samaritan, and hast a devil?
8:49 Jesus answered, I have not a devil; but I honour my Father, and ye do dishonour me.
8:50 And I seek not mine own glory: there is one that seeketh and judgeth. 8:51 Verily, verily, I say unto you, If a man keep my saying, he shall never see death.
8:52 Then said the Jews unto him, Now we know that thou hast a devil. Abraham is dead, and the prophets; and thou sayest, If a man keep my saying, he shall never taste of death. 8:53 Art thou greater than our father Abraham, which is dead? and the prophets are dead: whom makest thou thyself?
8:54 Jesus answered, If I honour myself, my honour is nothing: it is my Father that honoureth me; of whom ye say, that he is your God: 8:55 Yet ye have not known him; but I know him: and if I should say, I know him not, I shall be a liar like unto you: but I know him, and keep his saying.
8:56 Your father Abraham rejoiced to see my day: and he saw it, and was glad.
8:57 Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham?
8:58 Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.
8:59 Then took they up stones to cast at him: but Jesus hid himself, and went out of the temple, going through the midst of them, and so passed by." (John 8:31-59 KJV)
Fact Finder: What is the difference between a "covenant" and a "testament"?
See Covenant and Testament