The Redeemed Are Free
For freedom Christ has set us free; stand firm therefore, and do not submit again to a yoke of slavery. (Galatians 5:1 ESV)Those who have been redeemed were not redeemed just to go back into bondage to another form of slavery. If you have been redeemed, then you are truly free. Paul warns us, then, to be careful to guard our freedom. In the context of the book of Galatians, the slavery Paul warned against is bondage to the law, but the principle in this verse can be applied to any system of rules or regulations to which we might obligate ourselves. Leon Morris warns:
It is one of the curious things in life that Christians have all too often neglected this . . . . Again and again it is not liberty in Christ which has characerized believers, but strict conformity to some new rule they have made or found. This may involve a rigorous asceticism or the firm conviction that the way forward is by the observance of some sacramental discipline or the like.1The heart of the spiritual life of the redeemed is not rule keeping, because the redeemed are free. We are defined by Spirit-worked faith which produces love for God and love for other people, not obedience to regulations.
This doesn't mean we have licentious freedom. Licentiousness, after all, is just an outward expression of bondage to sin, something we left behind when we were redeemed. No, the freedom we have results in Spirit-worked obedience; it produces fruit, the fruit of the Spirit. Redemptive freedom is true freedom, but it’s also a freedom that is, in another sense, quite demanding. That’s why we find the state of the redeemed person described in another way, too.
The Redeemed Are Christ’s Slaves
Romans 6:22 tells us that the redeemed have been “set free from sin and have become slaves of God”. We are freed for freedom, yet freed to be slaves of God. It's intriguing paradox, especially as expressed in 1 Corinthians:
For he who was called in the Lord as a bondservant is a freedman of the Lord. Likewise he who was free when called is a bondservant of Christ.  You were bought with a price; do not become bondservants of men. (1 Corinthians 7:22-23 ESV)As redeemed people we are both freedmen and slaves—Christ's slaves. We are bought with a price, so we should remain free; we are bought with a price, so we belong to God and should serve him.
Or do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own,  for you were bought with a price. So glorify God in your body. (1 Corinthians 6:19-20 ESV)That the redeemed are bought with a price sets us free from slavish obligation to the law, but at the same time it obligates us to shun immoral behaviour and glorify God instead.
Putting It Together
How is it that we are, on the one hand, free people, and on the other, Christ's slaves? Somehow, being a slave of Christ is equivalent to being truly free. Perhaps it's because being Christ's slave is what frees us from sin's power over us. Belonging to Christ means being controlled by the Spirit rather than "the spirit that is now at work in the sons of disobedience." Maybe we are free because in the new life of the Spirit we obey our master from the heart. Maybe real freedom is obeying because we love the one who redeemed us and owns us.
The bottom line is that the redeemed are delivered to a life of freedom and, at the same time, delivered to a life of service to Christ.
1 Leon Morris, The Atonement: It's Meaning and Significance, page 126.