Gentiles or those of the nations of the world in unbelief trample spiritual Jerusalem from above, heavenly Jerusalem. Spiritually speaking born again believers have entered into Jerusalem, we are "spirits of just men made perfect" when we have been born again. But as Paul below tells us "the desolate hath many more children than she which has a husband" we, born again believers have Christ as our Husband, and are children of the promise, but the children of the promise, born of the Spirit are persecuted by those born of the flesh. It is in this manner spiritually speaking that Jerusalem is being trampled by those in unbelief. This is why Paul writes for us to "Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the free woman."
Hebrews 12:22-24 (KJV) But ye are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and to an innumerable company of angels, To the general assembly and church of the firstborn, which are written in heaven, and to God the Judge of all, and to the spirits of just men made perfect, And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than that of Abel.
Galatians 4:26-29 (KJV) But Jerusalem which is above is free, which is the mother of us all. For it is written, Rejoice, thou barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband. Now we, brethren, as Isaac was, are the children of promise. But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now.
Galatians 4:30 (KJV) 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.