Yes, I tend to take the Apostles at their word. And as your cited text is concerning Jerusalem...How does Paul contrast natural Jerusalem with spiritual Jerusalem? One is a bondwoman, and the other is free.
Citing the Scriptures as his authority, what does Paul say to do with the bondwoman?
Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall NOT be heir with the son of the freewoman. So then, brethren, we are not children of the bondwoman, but of the free. - Galatians 4:30-31 Paul is talking about being under the bondage of the ceremonial aspects of the law. He is warning Judaizers that salvation cannot be obtained by keeping the law of Moses. Those who mix law and grace (Seventh Day Adventists for example) have perverted the gospel of the grace of God (Gal 1:8-9). "I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain" (Gal 2:20). "Christ is become of no effect unto you, whosoever of you are justified by the law; ye are fallen from grace." (Gal 5:4).