How many children did Abraham have, one or two?
Genesis 22:2; Hebrews 11:17 and Galatians 4:22
One son
(Genesis 22:2) - "And He said, "Take now your son, your only son, whom you love, Isaac, and go to the land of Moriah; and offer him there as a burnt offering on one of the mountains of which I will tell you."
(Hebrews 11:17) - "By faith Abraham, when he was tested, offered up Isaac; and he who had received the promises was offering up his only begotten son."
Two sons
(Galatians 4:22) - "For it is written that Abraham had two sons, one by the bondwoman and one by the free woman."
The answer to this apparent contradiction is found in understanding the typological representation of Isaac, Abraham's second born son, as a type of Christ. Abraham had Ishmael by the handmaiden Hagar. But Isaac was the child of promise, not Ishmael: "But God said to Abraham, "Do not be distressed because of the lad and your maid; whatever Sarah tells you, listen to her, for through Isaac your descendants shall be named,'" (Gen. 21:12).
If you look at the chart below, you will see the similarities between Isaac and Jesus. In other words, Isaac was a prophetic representation of Jesus. This is why Jesus said, "Your father Abraham rejoiced to see My day, and he saw it and was glad," (John 8:56). Abraham had, in a very real sense, seen the gospel presentation in the offering of his son, his "only begotten." So, we see here that the term "only begotten" is in reference to the unique son of God and Isaac was acting out the sacrifice of Christ, prophetically.
ISAAC JESUS
Genesis Gospels
Only begotten Son Gen. 22:2 John 3:16
Offered on a mountain, hill Gen. 22:2 Matt. 21:10
Took donkey to place of sacrifice Gen. 22:3 Matt. 21:2-11
Two men went with him Gen. 22:3 Mark 15:27; Luke 23:33
Three day journey. Jesus: three days in the grave Gen. 22:4 Luke 24:13-21
Son carried wood on his back up hill Gen. 22:6 John 19:17
God will provide for Himself the lamb Gen. 22:8 John 1:29
Son was offered on the wood Gen. 22:9 Luke 23:33
Ram in thicket of thorns, crown of thorns. Gen. 22:13 John 19:2
The seed will be multiplied Gen. 22:17 John 1:12; Isaiah 53:10
Abraham went down. Son didn't. Isaac is "not mentioned"
Gen. 22:19 Luke 23:46
Servant, gets bride for son Gen. 24:1-4 Eph. 5:22-32; Rev. 21:2,9; 22:17
The bride was a beautiful virgin Gen. 24:16 2 Cor. 11:2
Servant offered ten gifts to bride Gen. 24:10 Rom. 6:23; 12; 1 Cor. 12
Also, Abraham had six other sons besides Ishmael and Isaac through his wife Keturah whom he married after Sarah died. "Now Abraham took another wife, whose name was Keturah. 2And she bore to him Zimran and Jokshan and Medan and Midian and Ishbak and Shuah," (Gen. 25:1-2). Obviously, this was known by the writers of Genesis as well as Hebrews and Galatians.