Gen 21:1 And the LORD visited Sarah as he had said, and the LORD did unto Sarah as he had spoken.
Gen 21:2 For Sarah conceived, and bore Abraham a son in his old age, at the set time of which God had spoken to him.
Gen 21:3 And Abraham called the name of his son that was born unto him, whom Sarah bore to him, Isaac.
Gen 21:4 And Abraham circumcised his son Isaac being eight days old, as God had commanded him.

When it came to the word of the Lordm Abraham obeyed God. This obedience showed the seriousness with which Abraham served God. In spite of lapses of faith and mistakes, His heart was right with God.

Gen 21:5 And Abraham was a hundred years old, when his son Isaac was born unto him.
Gen 21:6 And Sarah said, God hath made me to laugh, so that all that hear will laugh with me.
Gen 21:7 And she said, Who would have said unto Abraham, that Sarah should have given children suck? for I have born him a son in his old age.
Gen 21:8 And the child grew, and was weaned: and Abraham made a great feast the same day that Isaac was weaned.
Gen 21:9 And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking.

What Ishmael was doing here specifically is not stated but perhaps there is a little envy on the part of Ishmael causing him to mock. He was no longer the center of attention and adoration of Abraham. Ishmael was perfectly normal but he could have overcome jealousy by taking his rightful place fearing God as his father Abraham did.

Gen 21:10 Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac.

I do admit feeling sorry for Hagar and Ishmael for certainly all this happened to them and it was no fault of their own. It is a good case to argue against plural marriages for sure. Separating the two though was in the will of God. The seed of Ishmael even today hates the Jewish people. Only both receiving Jesus Christ and being filled with the Holy Spirit can change that hate into love.

Gen 21:11 And the thing was very grievous in Abraham's sight because of his son.
Gen 21:12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.
Gen 21:13 And also of the son of the bondwoman will I make a nation, because he is thy seed.

God made a nation of Ishmael because he was the Son of Abraham and God loved and respected the desires of Abraham's heart. Yet, Isaac was chosen and what God says must come to pass.

Gen 21:14 And Abraham rose up early in the morning, and took bread, and a bottle of water, and gave it unto Hagar, putting it on her shoulder, and the child, and sent her away: and she departed, and wandered in the wilderness of Beer-sheba.

This is probably one of the second hardest things that Abraham had to do in his lifetime. The hardest is coming up in chapters to follow when God tells Abraham to sacrifice his only son.

Gen 21:15 And the water was spent in the bottle, and she cast the child under one of the shrubs.
Gen 21:16 And she went, and sat her down over against him a good way off, as it were a bowshot: for she said, Let me not see the death of the child. And she sat over against him, and lifted up her voice, and wept.
Gen 21:17 And God heard the voice of the lad; and the angel of God called to Hagar out of heaven, and said unto her, What aileth thee, Hagar? fear not; for God hath heard the voice of the lad where he is.

God remember His promise to Abraham and took care of Hagar. How great is His love. Through Abraham, Isaac and Jacob the seed was to come that would bring salvation to every kindred, tongue and nation. Through Christ all are made free from sin and free from hate if we let Him. In Christ is the power to overcome prejudice and hate. We can have the love of God shed abroad in our hearts by the Holy Spirit. It is a new way and a new beginning for all who believe and receive this savior that Abraham looked forward to and we can look to now since we live in a day in which Jesus already came and paid the price to bring us this salvation promised to Abraham. It is true He came to the Jews first but now this salvation is offered to all who will simply believe in what He came to do. The message is to repent and believe the gospel of Jesus Christ.

Gen 21:18 Arise, lift up the lad, and hold him in thine hand; for I will make him a great nation.
Gen 21:19 And God opened her eyes, and she saw a well of water; and she went, and filled the bottle with water, and gave the lad drink.
Gen 21:20 And God was with the lad; and he grew, and dwelt in the wilderness, and became an archer.
Gen 21:21 And he dwelt in the wilderness of Paran: and his mother took him a wife out of the land of Egypt.

It is strange how that both the descendants of Ishmael and Isaac as a nation reject the one who was promised by God to save us from sin. Both sons were born to the one God chose to bring salvation to the whole world and yet the descendants of both sons reject the promised seed when He did come. 

The Gentile nations who didn't have any part of the earlier promises of God are the ones who believed after the Jewish people rejected Christ. We live in a day now that Jews are coming to Christ and the days of the Gentiles may be drawing to a close.

Gen 21:22 And it came to pass at that time, that Abimelech and Phichol the chief captain of his host spoke unto Abraham, saying, God is with thee in all that thou doest:

If we live godly, other people will see and may believe because of our own testimony and lifestyle.

Gen 21:23 Now therefore swear unto me here by God that thou wilt not deal falsely with me, nor with my son, nor with my son's son: but according to the kindness that I have done unto thee, thou shalt do unto me, and to the land wherein thou hast sojourned.
Gen 21:24 And Abraham said, I will swear.
Gen 21:25 And Abraham reproved Abimelech because of a well of water, which Abimelech's servants had violently taken away.
Gen 21:26 And Abimelech said, I know not who hath done this thing: neither didst thou tell me, neither yet heard I of it, but today.
Gen 21:27 And Abraham took sheep and oxen, and gave them unto Abimelech; and both of them made a covenant.
Gen 21:28 And Abraham set seven ewe lambs of the flock by themselves.
Gen 21:29 And Abimelech said unto Abraham, What mean these seven ewe lambs which thou hast set by themselves?
Gen 21:30 And he said, For these seven ewe lambs shalt thou take of my hand, that they may be a witness unto me, that I have digged this well.
Gen 21:31 Wherefore he called that place Beer-sheba; because there they swore both of them.
Gen 21:32 Thus they made a covenant at Beer-sheba: then Abimelech rose up, and Phichol the chief captain of his host, and they returned into the land of the Philistines.
Gen 21:33 And Abraham planted a grove in Beer-sheba, and called there on the name of the LORD, the everlasting God.
Gen 21:34 And Abraham sojourned in the Philistines' land many days.

There was previous fighting of wells of water that happened in this time and in the days of Isaac to come. Abimelech made a covenant with Abraham that was forgotten by others in later years. Abraham used this place to worship God. Others used groves to worship idols. I'm glad we live in a day that we can worship God anywhere by the spirit that He gives us when we believe in Jesus Christ, the Son of God. When we are born again by God's spirit we can then worship God anywhere and any time. We can now worship Him in spirit and in truth. We don't have to face east or west.  We don't have to be in a temple or shrine.  We don't have to be on a mountain.  We can worship God anywhere.  This was made possible by this new and living way God provided for us through the seed of Abraham.  God chose Abraham to bring us Himself.  God came in the flesh.  God became one of us.  God send His only Son to become flesh, live in human flesh yet without sin so that when He died, He died being innocent, not deserving death.  His death can count on our behalf if we believe this and receive it.  We can be made whole, born again by His spirit and walk in the newness of life through faith in Jesus. 

Here is how the apostle Paul explains the two children of Abraham and the two covenants.  One is by faith and the other the works of the law. 

Gal 4:22 For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.
Gal 4:23 But he who was of the bondwoman was born after the flesh; but he of the freewoman was by promise.
Gal 4:24 Which things are an allegory: for these are the two covenants; the one from the mount Sinai, which engendereth to bondage, which is Hagar.
Gal 4:25 For this Hagar is mount Sinai in Arabia, and answereth to Jerusalem which now is, and is in bondage with her children.
Gal 4:26 But Jerusalem which is above is free, which is the mother of us all.
Gal 4:27 For it is written, Rejoice, thou barren that bearest not; break forth and cry, thou that travailest not; for the desolate hath many more children than she which hath a husband.
Gal 4:28 Now we, brethren, as Isaac was, are the children of promise.
Gal 4:29 But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now.
Gal 4:30 Nevertheless what saith the Scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.
Gal 4:31 So then, brethren, we are not children of the bondwoman, but of the free.

Faith makes us free from the bondage and condemnation of the law.  The law was good but was only until the time Christ came to put the law in our hearts by His spirit.  Now we are free from the condemnation of the law and can live by the spirit which gives life.  Religion which just has laws and no way to escape sin or bondage from the law is just religion.  Jesus came to free us from all religious rituals that try to make us perfect people by our own works.  Instead He gives us His spirit that dwells within us teaching us to live for God out of love and joy.  This comes by faith.  We simply believe in Jesus and trust in Him instead of trying to "be good" on our own.  We accept His righteousness in place of our own righteousness which can never be good enough.  By faith the spirit is given to us to give us the desire to live holy because we love Him who is holy instead of trying to live holy by our own efforts.  We can now live and walk in the spirit instead of being in bondage to the flesh.  We now can give also because we love Him and not because of any tithing law.  If we love God's ministers, if we love the gospel, if we love the poor, if we love the work of God, we will give for that reason.  We don't have to be in bondage to any tithing law although 10 percent is a good guideline for those who have no idea what to give.  I don't believe in paying tithes but I do believe in giving tithes or whatever I purpose in my heart.  How much better it is to serve God out of love and joy instead of trying to earn salvation by good works.  The spirit if God frees us from this and makes us do things because we love God and are thankful for His salvation and promise of eternal life.  Jesus made this new way for us.  It is not a religion, it is a way of faith. 

Genesis 22