The Galatian believers, under the free woman, as it were, were at liberty and were now to stand in that liberty and not go back to the bondwoman.
Christ will not profit one who places himself under law, for such a one would be under the full requirements of the law, and Christ and His work are of no value to him. He is fallen from grace. To be once under grace and then return back to the law is to fall.
The believer in Christ is made the righteousness of God. Here he rests even as God does rest. We are waiting "for the hope of righteousness by faith."
A little leaven leavens the whole lump, thus the assembly is defiled.
The saints did once run well. Paul said, "Who did hinder you, that ye should not obey the truth?" He had confidence in them through the Lord that they would obey, and whoever troubled them would bear his judgment. The one who preached circumcision had no persecution. The world will accept that but will not accept free grace. Paul desired that those who troubled them would be cut off.
Being called unto liberty they should serve one another in love. In loving their neighbors as themselves the law was fulfilled. To walk in the Spirit was to not fulfill the lusts of the flesh. The doctrine of perfect grace was connected with a walk worthy of God's people without law.
We are hindered by the flesh when walking according to the Spirit, and the Spirit resists the working of the flesh to prevent it from doing what it would.
"The fruit of the Spirit is love, joy, peace, long-suffering, gentleness, goodness, faith, meekness, temperance: against such there is no law." The law cannot be a rule of life for the believer. We walk by faith which means to have the Word alone applied to our hearts and consciences and to our pathway.
To be filled with the Spirit supposes that the flesh is set aside. This will bring the fruit of the Spirit rather than the fruits of nature or the flesh. To be taken up with that which has no spiritual purpose or value is going back to the flesh.