We'll just have to disagree -though I should point out that you did not actually answer the question (Then why will the whole world keep the feast of tabernacles?)
You can't be in Christ if you do not obey the law -and keeping the holy days is part of the first commandment -not to mention the specific commandment about the weekly sabbath.
Romans 3:31
Do we then make void the law through faith? God forbid: yea, we establish the law.
I strongly suggest you reconsider teaching that people should not keep the commandments of God.
Matt 5:19
Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach
them, the same shall be called great in the kingdom of heaven
The Test of Knowing Him
3 Now by this we know that we know Him, if we keep His commandments. 4 He who says, “I know Him,” and does not keep His commandments, is a liar, and the truth is not in him. 5 But whoever keeps His word, truly the love of God is perfected in him. By this we know that we are in Him. 6 He who says he abides in Him ought himself also to walk just as He walked.
this dos not support what you say. You are basing you doctrine on the self proclaimed apostle Paul the liar and murderer
I Cor 5:8
…
7Clean out the old leaven so that you may be a new lump, just as you are in fact unleavened. For Christ our Passover also has been sacrificed.
8Therefore let us celebrate the feast, not with old leaven, nor with the leaven of malice and wickedness, but with the unleavened bread of sincerity and truth.