Galatians 4

As some of the converted Galatians began to return to the law of Moses, Paul compares the two as being free versus being in bondage asking -

"...now, after that ye have known God, or rather are known of God, how turn ye again to the weak and beggarly elements, whereunto ye desire again to be in bondage?" (New Testament | Galatians 4:9)

After comparing the law of Moses to Abraham's bondmaid and the gospel of Jesus Christ to Sarah as a freewomen or one or the promise of "joint-heir", Paul instructs -

"...Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.
31 So then, brethren, we are not children of the bondwoman, but of the free." (New Testament | Galatians 4:30 - 31)

For -

"...we, brethren, as Isaac was, are the children of promise." (New Testament | Galatians 4:28)

And then Paul teaches what it really means to be "children of promise" or "joint-heirs" to being in bondage -

"STAND fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage." (New Testament | Galatians 5:1)

He compares the yoke of bondage to the natural man or the works of the flesh teaching -

"Walk in the Spirit, and ye shall not fulfil the lust of the flesh.
17 For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
18 But if ye be led of the Spirit, ye are not under the law." (New Testament | Galatians 5:16 - 18)

Being in the yoke of bondage or not keeping the commandments keeps one from being a "joint-heir" for -

"...the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness,
20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies,
21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God." (New Testament | Galatians 5:19 - 21)

Including being -

"...desirous of vain glory, provoking one another, envying one another." (New Testament | Galatians 5:26)

What is liberty or being free? It is to "walk in the Spirit" or live such that you have the Holy Ghost for -

"...the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith,
23 Meekness, temperance: against such there is no law.
24 And they that are Christ's have crucified the flesh with the affections and lusts." (New Testament | Galatians 5:22 - 24)

Therfore -

"If we live in the Spirit, let us also walk in the Spirit." (New Testament | Galatians 5:25)

This is what is meant by having faith in Christ!