The difference between believers who rested in Christ only, and those who trusted in the law, is explained by the lives of Isaac and Ishmael. These things are an example and the Spirit of God points out something further. Hagar and Sarah are examples of the new and old covenant. The heavenly Jerusalem, the true church from above, represented by Sarah, is in a state of freedom, and is the mother of all believers, who are born of the Holy Spirit.
They were by regeneration and true faith, made a part of the true seed of Abraham, according to the promise made to him.
Hagar is of the earth, always fighting for survival receiving their reward while on earth and never taking it into eternal life. A life of torment – never being good enough.
So then, we are not children of the bond-woman, but of the free. We would not have found out this example in the history of Sarah and Hagar, if it had not been shown to us, and this is what was intended by the Holy Spirit. It is an explanation of the subject, not an argument in proof of it. This is God's way and what we do with this will not change Him, however what we do with this will change us.
The first covenant spirit is of bondage to sin and death. The second covenant spirit is of liberty and freedom; not liberty to sin, but liberty in and to duty. The first is a spirit of persecution; the second is a spirit of love. Let us rest our souls on the Scriptures in a gospel of hope and cheerful obedience, show that our conversation and treasure are indeed in heaven.
1 Let us go forward, then, to mature teaching and leave behind us the first lessons of the Christian message. We should not lay again the foundation of turning away from useless works and believing in God; 2 of the teaching about baptisms and the laying on of hands; of the resurrection of the dead and the eternal judgement. 3 Let us go forward! And this is what we will do, if God allows. 4 For how can those who abandon their faith be brought back to repent again? They were once in God's light; they tasted heaven's gift and received their share of the Holy Spirit; 5 they knew from experience that God's word is good, and they had felt the powers of the coming age. 6 And then they abandoned their faith! It is impossible to bring them back to repent again, because they are again crucifying the Son of God and exposing him to public shame. 7 God blesses the soil which drinks in the rain that often falls on it and which grows plants that are useful to those for whom it is cultivated. 8 But if it grows thorns and weeds, it is worth nothing; it is in danger of being cursed by God and will be destroyed by fire. 9 But even if we speak like this, dear friends, we feel sure about you. We know that you have the better blessings that belong to your salvation. 10 God is not unfair. He will not forget the work you did or the love you showed for him in the help you gave and are still giving to other Christians. 11 Our great desire is that each of you keep up your eagerness to the end, so that the things you hope for will come true. 12 We do not want you to become lazy, but to be like those who believe and are patient, and so receive what God has promised. 13 When God made his promise to Abraham, he made a vow to do what he had promised. Since there was no one greater than himself, he used his own name when he made his vow. 14 He said, "I promise you that I will bless you and give you many descendants." 15 Abraham was patient, and so he received what God had promised. 16 When we make a vow, we use the name of someone greater than ourselves, and the vow settles all arguments. 17 To those who were to receive what he promised, God wanted to make it very clear that he would never change his purpose; so he added his vow to the promise. 18 There are these two things, then, that cannot change and about which God cannot lie. So we who have found safety with him are greatly encouraged to hold firmly to the hope placed before us. 19 We have this hope as an anchor for our lives. It is safe and sure, and goes through the curtain of the heavenly temple into the inner sanctuary. 20 On our behalf Jesus has gone in there before us and has become a high priest forever, in the priestly order of Melchizedek.
Number 1; The promise of God to Abraham did more than give civilisation to men; it opened to them the doors of heaven. Great as the temporary gifts have been from it, greater and better are its spiritual blessings. The best commentary that has ever been written on the promise made to Abraham is to be found in Hebrews 6. It points to the glorious character of this spiritual promise. "God, is patient, for God is eternal," and so also the faith that trusts the promise of God partakes of the unchangeable calm of Him on whom it rests, the same yesterday, today, and for ever. Canaan, the heavenly Canaan, was ever before the ancient saints and they saw that it was set on the top of the cross.
Number 2; We too are children of promise; but often we forget this, and set our hearts on some earthly Canaan. We shall find that the only rest it will give us is the rest of the grave and more than likely in hell. The goal that is set before us and the feebleness of all human effort to reach it and our happiness on earth should consist rather in working than in enjoying, rather in using the means given to us, than in gaining the end. If this is not so and we die, the outlook before us would be sad and gloomy with the possibility of missing heaven. But to us it has been given to know Christ and the power of His resurrection. His risen body sheds the true light upon life and its work; it fulfils to us all the promise of good fortune, and adds to its fulfilment the glories of eternity. Our God wants us to be about His work of the resurrection.
Number 3; I know that it is popular today to say “God told me or God gave me a word”, etc. etc. When we read the Bible it is plain that God has called all His children to bear witness of His glory – this is not an option – it is a command from God. God is not so much interested in where you – He is interested in how you obey Him where you are. Don't live like it is your last day on earth – live like a child of the promise. Don't glory in who you are, glory in God as you live out your mission on earth.