God’s faithfulness does not do away with his discipline. God disciplines the sons that he loves. When we sin, God’s discipline comes to us in the form of reaping what we have sown. “Do not be deceived: God is not mocked, for whatever one sows, that will he also reap” (Gal. 6:7). Abraham is a case study of this principle.

At the time of Isaac’s weaning (Gen. 21) Ishmael was somewhere between 15 and 16. Abraham loved Ishmael. He probably thinks that God’s promises will now come to pass through both Ishmael and Isaac. But that is and has never been God’s plan.

On the day of Isaac’s weaning, strife erupts between Sarah and Hagar. Sarah does not want her son to share the inheritance with Hagar’s son. For fifteen years there has been bad blood between Sarah and Hagar. (It started in Gen 16). It culminates in Genesis 21.

(Genesis 21:8–11) “8 And the child grew and was weaned. And Abraham made a great feast on the day that Isaac was weaned. 9 But Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, laughing. 10 So she said to Abraham, “Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac.” 11 And the thing was very displeasing to Abraham on account of his son.”

Sin doesn’t always produce a reaping. Sometimes God is merciful, and there is little or no reaping. (Think Pharaoh and Abimelech). That is not the case here. The reaping is deep, painful, and prolonged. It will mean heartbreak at Abraham’s separation from Ishmael, and it will mean enmity between the children of Ishmael and the children of Isaac for millennia.
First, it will mean separation from Ishmael. God asks Abraham to reject his son through Hagar. But Abraham loves Ishmael. Ishmael has been his only heir for fifteen years. Abraham has convinced himself that all of God’s promises will come through Ishmael. In fact, when Ishmael was about 13 or 14, and Abraham was 99, God came to our hero and told him that Sarah is going to have a son. Here is how Abraham reacts.
(Genesis 17:18) “And Abraham said to God, “Oh that Ishmael might live before you!””
He doesn’t want a son through Sarah. Why does Abraham feel this way? He loves Ishmael. He has invested himself in Ishmael. He has trained him as only a father who receives an only son in his old age would train him. He has doted on him. He is happy with Ishmael. He loves Ishmael. That is why when Sarah tells her husband, “Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac.” The text ends—11 And the thing was very displeasing to Abraham on account of his son.”
However, Abraham is a man of God. Because we feel his pain, we are astounded when he acts so decisively the next morning.
(Genesis 21:14) “14 So Abraham rose early in the morning and took bread and a skin of water and gave it to Hagar, putting it on her shoulder, along with the child, and sent her away. And she departed and wandered in the wilderness of Beersheba.”
Since the beginning separation from those that he loves has characterized Abraham’s relationship with God. In fact, this theme permeates the Bible. (Luke 14:25–27) “25 Now great crowds accompanied him, and he turned and said to them, 26 “If anyone comes to me and does not hate his own father and mother and wife and children and brothers and sisters, yes, and even his own life, he cannot be my disciple. 27 Whoever does not bear his own cross and come after me cannot be my disciple.”
First at Abraham’s call God asked him to separate from his family, his clan, his father’s house and the country of his birth. Then later God asked him to separate from Lot. Now God commands him to separate from Ishmael. Ultimately, God will even ask Abraham to put God between himself and Isaac.

Brothers and sisters, it is the same with us. God will have no competing god’s in our lives. He expects us to love him so much more than those close to us that our love for them is like hatred compared to our love for God. So, he must reject Ishmael the child of his unbelief. He must reap what he has sown.
Second, subsequent generations will also reap Abraham’s unbelief. The effects of sin are always social. They are like a virus. They seldom stay confined to the sinner. They attack our spouses, children or room-mates. Ultimately, Ishmael will become the father of the Arabs. In fact, the Moslems actually trace their descent to Abraham through Ishmael. This is a problem. The character of Ishmael and his descendants has not been attractive.

God prophesied this in Genesis 16. After Ishmael was conceived, Hagar began to look down on Sarah, so Sarah sent her away pregnant. Hagar wandered in the desert, and the angel of the Lord came to her.

(Genesis 16:11–12) “11 “Behold, you are pregnant and shall bear a son. You shall call his name Ishmael, because the LORD has listened to your affliction. 12 He shall be a wild donkey of a man, his hand against everyone and everyone’s hand against him, and he shall dwell over against all his kinsmen.””

Verse 12 is a picture of the Islamic people today. Picture the Arabs on TV in a frenzied state, screaming and yelling, throwing dirt in the air, firing their rifles in the air.

In fact, today’s Jews are reaping Abraham’s sin through the intense hostility of Ishmael’s descendants.

From Abraham’s story we can learn the importance of the fear of God. We reap what we sow, and God is behind the reaping. Brothers and sisters, let us cultivate the fear of God.