We do. Christians keep the New Covenant with Christian understanding. God's law was never going to be "done away with" unless heaven and earth passed away (Matthew 5:18. ...please check outside for verification that God's law is not yet done away. And, "All" written in the "Law" has not yet been "fulfilled"--including the LORD's return--, which is yet another stinky argument by weaselous "experts" of the Bible, who "expertly" pursuade people to not keep God's Law. Jesus foretold these heretics: Matthew 5:29 Whosoever therefore shall break one of these least commandments, and teach men so, he shall be called least in the kingdom of heaven: but whosoever shall do and teach them, the same shall be called great in the kingdom of heaven--KJV) Hebrews 8:7-12 The New Covenant is based on God's Holy Spirit, which puts "My laws in their mind and write them on their hearts..." The New Covenant makes people keep God's laws PURER and BETTER and WITH MORE ZEAL and TRUE LOVE. It makes God's law HONORABLE and SPIRITUAL...Jesus said that a man shouldn't even look at a woman to lust after her...! God is looking for children to become "Spiritual Jews", who will keep the law with their whole hearts Romans 2:28-29. Remember, Jesus warned his disciples to beware, not of the Pharisee's keeping of His Law, but the Pharisee's BREAKING THE LAW WHILE APPEARING TO KEEP THE LAW! Matthew 23 is but one example.)
Keeping the Feast of Tabernacles is an exceptional blessing, yet takes preparation. A tenth part of income is saved for keeping the Feasts of God (Deut. 14:22-23). A "tabernacle" can be any temporary dwelling; for example, a tent, R.V. hotel room, condominium, or even exchanging homes with a friend qualifies. (Example: The Tabernacle of the Covenant was a tent: portable and temporary, yet certainly not flimsy, leaky, nor lacking quality.) The dwelling's temporary-ness helps Christians understand that they really are to be "strangers and pilgrims" on an adventure in this world! God's people assemble every year, at Feast of Tabernacles (and all the Feasts which the Lord commanded and kept), in many locations ALL OVER THE WORLD, to worship God and "rejoice", attending Christian church services.
As all of God's Holy Days, the Feast of Tabernacles has a prophetic purpose: it portrays a New Testament event. It falls 14 days after the Feast of Trumpets (picturing Christ's Return) and 5 days after the Day of Atonement (portraying the banishing of the devil), the 7 day Feast of Tabernacles pictures God's establishment of His Final, Perfect Government on this earth.