Here begins a lengthy series on David, and of course Jesus. We begin with the genealogy of David. This is from the end of the book of Ruth:
Now, these are the generations of Perez: Perez fathered Hezron, Hezron fathered Ram, Ram fathered Amminadab, Amminadab fathered Nashon, Nashon fathered Salmon, Salmon fathered Boaz, Boaz fathered Obed, Obed fathered Jesse, and Jesse fathered David. (Ruth 4:18-22)
If we look at Christ's genealogy from the first chapter of Matthew, we see something interesting:
"Salmon the father of Boaz by Rahab, and Boaz the father of Obed by Ruth." (Matthew 1:5)
Twice in a row, in Christ's (and David's) genealogy, men from Israel have married gentile women, incorporating "unclean" foreigners into the bloodline. This is especially important, because Christianity, or true Israel, is not limited to the bloodline of Abraham. Indeed, outsiders are grafted into the true vine. Hear what Paul says in Romans 11.
But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. Then you will say, “Branches were broken off so that I might be grafted in.” That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but fear. For if God did not spare the natural branches, neither will he spare you. Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness. Otherwise you too will be cut off. And even they, if they do not continue in their unbelief, will be grafted in, for God has the power to graft them in again. For if you were cut from what is by nature a wild olive tree, and grafted, contrary to nature, into a cultivated olive tree, how much more will these, the natural branches, be grafted back into their own olive tree. (Romans 11:17-24)
Even though the genealogy comes before Christ, it ends with Christ, and we can look back and see that the root is in fact Christ--remember he was begotten of God before all worlds--and so the ancestry is purposefully selected by God, who knew the bloodline beforehand. So Ruth was chosen by God. Rahab was chosen by God. Likewise, after Christ there is a spiritual "adopted" genealogy by faith alone that includes all believers. Christ is the root and all believers are the branches. Paul tells us to stand fast through faith, for wild and natural branches can not only be grafted in but removed at God's will.
Faith alone. Hebrews 11:31 says, "By faith Rahab the prostitute did not perish with those who were disobedient, because she had given a friendly welcome to the spies." By faith she chose Christ over the world. The scarlet thread she hung in the window to save her and her family's life was Christ. James 2:25 says that Rahab the prostitute was justified by works and not by faith alone. But when we read Joshua 2 we find that her work was completely grounded in faith. She acted completely on faith. She had faith in Israel that she would not be destroyed along with the rest, and so she acted accordingly, even though by all rational means, the people of Jericho would be more dangerous to one who betrayed them than the unlikely fall of the great walls by a group of people on foot who marched around and shouted at the walls. Rationality tells Rahab to betray the spies and go with her own people. Faith tells Rahab to save the spies and lie to her people.
Here's Joshua 6:23: "So the young men who had been spies went in and brought out Rahab and her father and mother and brothers and all who belonged to her. And they brought all her relatives and put them outside the camp of Israel." Although they were outside the camp of Israel, outsiders, Salmon extended his hand to Rahab and married her. Then they fathered Boaz in the line of David and Christ. Likewise, Ruth was "outside the camp," a Moabite woman brought to Israel by the mother of her dead husband. Through faith in Naomi's words, Ruth found herself in a place where Boaz could extend his hand to her and marry her. They fathered Obed in the line of David and Christ.
Things we need to remember along the lines of the doctrines of grace:
1. To God, we are all prostitutes. To God, we are all Moabites. Remember the Moabites were spawned by illicit relations between Lot and his daughters. We all come from a corrupt bloodline.
2. God saves us anyway. He is rich in kindness and elects us without conditions into his family. No matter where we are from. No matter what evil we have done.
3. Christ died on behalf of branches that grew naturally on his tree, and he died for wild branches that were grafted on later. Also, there are natural branches on the tree that have been removed and are not covered by the atonement. There are, of course, wild branches that are never grafted on.
4. Rahab and Ruth did not graft themselves onto the root of Christ. God grafted them. They did the right thing because they were irresistibly drawn to the truth in Jesus Christ.
5. Rahab and Ruth persevered to the end, since Jesus was begotten before all worlds. His human genealogy was known to our Lord. God knew Rahab and Ruth from the beginning and he provided not only the protection of life they needed to be permanently grafted onto the vine, but he also provided the narrow course they needed to follow to get there. As children of God, he will never let us fall.