For God’s children, the result of receiving grace is freedom, a life of joyful liberty springing from the assurance that God’s condemnation toward us has forever been put away by Christ. Paul tells us that our status has changed from slaves, who live in constant fear that God will cast us out of his presence because of our failure to keep the law, to beloved sons, who remain in the house forever by virtue of our identity in Christ.
The problem with all this – the Gospel, adoption, freedom – is that we don’t believe its true. It seems too good to be true, at least for us. So rather than resting in grace and the sufficiency of Christ, we feel on much safer ground trying to earn God’s favor by feverishly striving to keep the law. We “want to be under the law,” and “want to be its slaves once more.” (Gal 4:21a, 4:9) The result is that on the days when we feel good about our law-keeping, we swell with pride, sure that God loves us more, but on the days when we fail, we are plunged into despair, because we’re sure it’s all over for us. So the sons of God, who have been set free by Christ, have willingly returned to a life of slavery under the law. (Gal 4:8-10)
Paul tells us that this problem is nothing unusual, and that we must make daily work of fighting for our freedom: “For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery.” (Gal 5:1) Here’s Luther:
“This freedom is not given us by the law or because of our righteousness, but freely for Christ’s sake. Paul says this throughout the whole letter. Christ also, in John 8:36, “If the Son sets you free, you will be free indeed.” Only he comes between us and the evils that trouble and afflict us; he has overcome them and has taken them away, so that they cannot oppress or condemn us anymore. Instead of sin and death, he gives us righteousness and everlasting life; and in this way he changes the slavery and terrors of the law into freedom of conscience and the consolation of the Gospel (Matthew 9:2).
Reason cannot grasp how wonderful this is. When we consider it spiritually, we see that it is inestimable to have God merciful and favorable forever. It is impossible for people who seek to win heaven, life, and salvation by their own actions and merits to know what freedom and deliverance from sin is. But our freedom is founded on Christ himself, seated at God’s right hand and interceding for us. Therefore, the forgiveness of sins, righteousness, life, and freedom that we have through him are sure, certain, and perpetual. If we cling to Christ with steadfast faith and stand firm in the freedom he has given us, we shall obtain those inestimable gifts; but if we are careless and negligent, we shall lose them in some way. It is not without cause that Paul tells us to watch and stand firm, for he knew that the devil seeks nothing more than to despoil us of this freedom that cost Christ so much and to burden us again by his ministers with slavery.”
Martin Luther, Galatians. The Crossway Classic Commentaries (Wheaton, IL: Crossway, 1998), 243.