Consider this passage in light of the laws and beliefs that we frequently point to as setting us apart from the world. A person can keep the Sabbath, at least in the letter, and still display drunkenness, hatred, contentions, outbursts of wrath, and dissensions. One can reject the Trinity doctrine, the doctrine of eternal security, and the immortality of the soul yet promote and practice heresies, since a heresy is simply any deviation from truth. An individual can tithe yet exhibit selfish ambitions, envy, and jealousy. Someone can observe the laws of clean and unclean meats and still be unclean in his heart and in the decency of his life. A man can be physically pure in his relationships while living vicariously through revelries, which Adam Clarke's commentary defines as wild parties and obscene music.
The warning at the end of verse 21 is explicit: Those who practice such evils or make them a part of their lives will not be in God's Kingdom—they simply would not fit in. Their lifestyle is contrary to the quality of the life God lives and expects His children to live.
To put this another way, what kind of witness does a person make who keeps the Ten Commandments (including the Sabbath and holy days), eats only clean meats, tithes faithfully, and rejects false doctrines, yet has a temper, curses, tells dirty jokes, has a perpetual chip on his shoulder, always has a complaint against another, always looks out for "number one," drinks too much, and revels in perverse entertainment? Such a witness of nominal lawkeeping is useless to God, just as ancient Israel's witness to the nations gave the enemies of God an occasion to blaspheme (Ezekiel 36:20-23).
When Jesus Christ introduces Himself in the letter to the Laodicean church (Revelation 3:14), He highlights the fact that He is "the Faithful and True Witness." He points to this title to show where the Laodiceans fall short. They are so enamored of the world and so much a part of it that it is difficult for an observer to tell them apart from the rest of Babylon! Their lives do not glorify God because they do not demonstrate a separation from the world. They do not demonstrate holiness or sanctification.
In contrast, the result of the Holy Spirit being active in a person's life will be love, joy, peace, longsuffering, kindness, goodness, faithfulness, gentleness (meekness), and self-control (Galatians 5:22-23). These attitudes are not manifested all at once, which is why Paul calls them "fruit." Fruit takes time to develop and mature. Nevertheless, one whose life God dominates, who is led by His Spirit, will be exhibiting these things in addition to obeying God's law. He will be not merely obeying but also imitating God. He will be exhibiting these characteristics because he is a regenerated son of God who expresses the traits of his Father.