If the reader has time, he ought to read Luther's Commentary of Galatians on these verses. Galatians was Luther's favorite book of Scripture. His comments are so pertinent and instructive. We shall quote from Luther here and there but, or course, our quotations must be limited.
Verses 1-7 differ in no way in doctrine from 3:22-29. The only difference is in the literary figures which Paul uses. In 3:22-29 Paul spoke of from imprisonment to inheritance. In 4:1-7 he speaks of from slavery to inheritance. What do they have in common? From bondage to freedom.
Why does Paul state and restate under different figures? Because of the opinio legis, salvation by works, is such a stubborn and strong part of our sinful nature. Read all of John 8. The Jewish authorities battled Jesus and finally wanted to kill Him because they were work righteous. We are tempted to think, when we read Luke 18:9-14, that we ought thank God because we are not like that self-righteous Pharisee. But, by so doing, we are just like him and throw ourselves back under the bondage of the Law.
The Bible never calls the Law an evil thing. It is holy and just and good. God is its Author. The final objective of both Law and Gospel is the salvation of mankind. But, Law and Gospel are totally different in function.
The Gospel says: "Done." The Law says: "Do."
Verses 4 and 5 comprise one sentence, a complex adverbial sentence. It begins with a temporal clause. Then comes the main clause, beginning with "God sent..." Verse 5 comprises two purpose clauses which modify why "God sent."
"But when the time had fully come" simply means "the full time." "When God wills it." Leave it at that.
"Sent" means "to send out with a commission."
"His Son" denotes the divinity of Jesus. He pre-existence is implied.
Does "born of a woman" denote the virgin birth? Luther and others say it does. Others say it doesn't. How will you handle this in a Bible class?
"Born under the Law" shows the humanity of Jesus. These words lead us right into the vicarious atonement.
Luther: The Law did everything to Jesus that it did to us. It accused us and terrified us. It subjected us to sin, death, and the wrath of God; and it condemned us with its judgment . . . . It accused Him of blasphemy and sedition; it found Him guilty in the sight of God of all the sins of the entire world; finally it so saddened and frightened Him that He sweat blood, Luke 22:44; and eventually it sentenced Him to death, even death on a cross, Philippians 2:8.
Space does not allow further beautiful quotes from Luther. It is time well spent for the reader to peruse his Commentary on Galatians.
Here are two purpose phrases. Compare this with Galatians 3:14 where we also have two purpose phrases. In fact there is a close relationship between 3:10-14 and 4:1-7. Read the two side by side and note how the vicarious, universal atonement is so prominent in both passages.
Compare the two clauses in 3:14 and 4:5.
The first pair of clauses: Why did Christ redeem us from the curse of the Law? "In order that Abraham's blessing (the Gospel) in Christ Jesus might come to the nations (3:14)." Why did God send His Son into the world? "In order that he might redeem those under the Law (the cursed, all men) 4:5." This is clearly objective justification.
Now the second pair of clauses: In 3:14 it reads "In order that we might receive the promised Holy Spirit (the Gospel) by faith." In 4:5 we read: "In order that we might receive the adoption of sons." These purpose clauses are what we call subjective justification.
In 3:10-14 Paul was discussing the awful danger of salvation by works. In 4:1-7 Paul is speaking about passing from the bondage under the Law to the freedom under the Gospel.
Now, just one quote from Luther.
Luther: Now since Christ has conquered the Law in His own Person, it necessarily follows that He is God by nature. For except for God no one, neither a man nor an angel, is above the Law. But Christ is above the Law, because He has conquered and strangled it. Therefore He is the Son of God, and God by nature. If you grasp Christ as He is described by Paul here, you will neither go wrong nor be put to shame. Then you will be in a position to judge about all the various styles of life and about the religion and worship of the whole world. But if this true picture of Christ is removed or even obscured, there follows a sure confusion of everything; for the unspiritual person cannot judge about the Law of God . . . . Then what is the purpose of the Law if it does not justify? The final cause of the obedience of the Law by the righteous is not righteousness in the sight of God, which is received by faith alone, but the peace of the world, gratitude toward God, and a good example by which others are invited to believe the Gospel.
Note that in verse 5a Paul spoke of mankind in the third person, in 5b in the first person plural. In verse 6 he speaks of Christians in the second person plural. In verse 7 he speaks of Christians in the second person singular.
"Because" in verse 6 is variously translated "because" or "to prove that you are sons" or "inasmuch as." The word denotes both cause and evidence. God sends His Spirit into our hearts because Jesus took our place under the Law. God sends His Spirit into our hearts as evidence of the fact that we are redeemed. Read Galatians 3:1-5.
Paul's first Scriptural argument about justification by faith is by experience, of course, not apart from the means of grace. Faith is never a religious, charismatic, subjective experience apart from the Word of God and the atonement.
But God does give the Christian experiential evidence. What is the evidence? The Holy Spirit praying in the heart of the believer. And the greatest prayers are like those of Jesus: "Abba, Father." True prayer proves that there is saving faith. Saving faith proves that the individual is a son of God, a free man, and an heir of God and of Christ.
Note carefully the Trinity in this verse. The Bible always speaks of the Trinity as a saving God, in many, many places. Look at Matthew 28:19; 2 Corinthians 13:13.
Note that the Holy Spirit proceeds not only from the Father but also from the Son. This is one of the proof passages for the filioque principle, which means "and from the Son." Look at the Nicene Creed. The Father and the Son send the Holy Spirit into the heart of the repentant sinner to assure that sinner of forgiveness of sins. When that happens that sinner prays: "Abba, Father!"
Redemption from condemnation of Law, reception of sonship, and the gift of the Spirit, are a unit. Never separate them. They stand or fall together.
Now comes the grand conclusion in the form of two fact conditions.
"Therefore" in view of everything that's been said since Galatians 3:6 where Paul began by discussing the faith of Abraham and thus introduced the Scriptural arguments about justification by faith. Note that "you" is second person singular. "No longer a slave but a son" which means "you are no longer under the bondage and condemnation of the Law but you are free from sin, death, and the devil because Christ, your Substitute, suffered in your stead."
But more than that. A second conditional sentence which also goes back at least to 3:29: "If you are Christ's then you are Abraham's seed, heirs according to the promise." The last part of 4:7 is saying that the free person, the believer (see John 8:36) is an heir of everlasting life through the God who redeemed him.
Luther: The Holy Spirit was sent first in a manifest and visible form, Acts 2:3. This was the first sending forth of the Holy Spirit; it was necessary in the primitive church, which had to be established with visible signs on account of the unbelievers, as Paul testifies. 1 Corinthians 14:22: 'Tongues are a sign, not for believers but for unbelievers.' But later on, when the church had been gathered and confirmed by these signs, it was not necessary for this visible sending forth of the Holy Spirit to continue. The second sending is that by which the Holy Spirit, through the Word, is sent into the hearts of believers, as is said here: 'God has sent the Spirit of His Son into your hearts.' This happens with a visible form, namely, when through the spoken Word we receive fire and light, by which we are made new and different, and by which a new judgment, new sensations, and new drives arise in us . . . . Let everyone accustom himself, therefore, to believe for a certainty that he is in a state of grace and that his person with its works is pleasing to God . . . . Therefore we should strive daily to move more and more from uncertainty; and we should make an effort to wipe out completely that wicked idea which has consumed the entire world, namely that a person does not know whether they are in a state of grace. For if we are in doubt about our being in a state of grace and about our being pleasing to God for the sake of Christ, we are denying that Christ has redeemed us and completely denying all His benefits . . . The Holy Spirit's cry in us vastly exceeds, and breaks through, the powerful and horrible cries of the Law, sin, death, and the devil. It penetrates the clouds and heaven, and it reaches all the way to the ears of God . . . . In deep terrors and conflicts of conscience we do indeed take hold of Christ and believe that He is our Savior. . . . And this is our foundation: The Gospel commands us to look, not at our own good deeds or perfection but at God Himself as His promises, and at Christ Himself, the Mediator. By contrast the pope commands us to look, not at God as He promises, not at Christ our High Priest, but at our own works and merits . . . . And this is the reason why our theology is certain: it snatches us away from our selves and places us outside ourselves, so that we do not depend on our own strength, conscience, experience, person, or works but depend on that which is outside ourselves, that is, on the promise and truth of God, which cannot deceive. . . . For in the matter of justification I must be ignorant of the divine Law and not permit it to rule in any way over my conscience . . . . Therefore we come to these eternal goods -- the forgiveness of sins, righteousness, the glory of the resurrection, and eternal life -- not actively but passively. Nothing whatever interferes here; faith alone takes hold of the offered promise.