“Be of the same mind toward one another. Do not mind high things, but condescend to men of low estate. Do not be wise in your own conceits.” Romans 12:16“This I say then, walk in the Spirit, and you will not fulfill the lust of the flesh. For the flesh lusts against the Spirit, and the Spirit against the flesh: and these are contrary to one another: so that you cannot do the things that you have in mind. But if you are led of the Spirit, you are not under the law. Now the works of the flesh are manifest, which are these; adultery, fornication, uncleanness, lasciviousness, idolatry, witchcraft, hatred, contention, jealousies, wrath, strife, seditions, heresies, envy, murder, drunkenness, reveling, and things like this: of which I tell you now, as I have told you in time past, that they who exercise and practice such things will not inherit the Kingdom of God. But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance: against such there is no law. And they that belong to the “anointed one” (Christ) have crucified the flesh with the affections and lusts. If we live in the Spirit, let us also walk in the Spirit. Let us not glory without reason, challenging one another, envying one another.” Galatians 5:16-26
Joy. Most people confuse joy and happiness, and for good reason.
Happy - Being in the enjoyment of agreeable sensations from the possession of good; enjoying pleasure from the gratification of appetites or desires. The pleasurable sensations derived from the gratification of sensual appetites render a person temporarily happy; but he only can be esteemed really and permanently happy who enjoys peace of mind in the favor of God. To be in any degree happy we must be free from pain both of body and of mind; to be very happy we must be in the enjoyment of lively sensations of pleasure, either of body or mind.Joy - The passion or emotion excited by the acquisition or expectation of good; that excitement of pleasurable feelings which is caused by success, good fortune, the gratification of desire or some good possessed, or by a rational prospect of possessing what we love or desire; gladness; exultation; exhilaration of spirits. JOY is a delight of the mind, from the consideration of the present or assured approaching possession of a good.
I suppose you could say that happiness is more dependent upon one's present circumstances, and joy is more of a hopeful happiness. One is fleshly, and the other is spiritual. They are similar, but function differently. Happiness is solely dependent upon external circumstances where joy functions in good and bad circumstances. Why are the humble joyful?
The answer can be found in the source of their joy. God Himself. Now don't think that I am saying that the "only" thing the humble possess is joy. In this world we all are a combination of joy and sorrow. We live in the "Land of the Knowledge of Good and Evil," where pain, sorrow, and death abide. Sure, we have a hope, and it is in the person and work of Jesus the "anointed one." This is the hope that drives the true follower of Christ.
Our God is infinite, Sovereign, holy, Triune, omniscient, faithful, loving, omnipotent, self-existent, self-sufficient, just, immutable, merciful, eternal, good, gracious, patient, and omnipresent. We have every reason to have fear, hope, and joy in a God like that. There is no altar, no craft that men can employ that can top Him. All of the gods of the earth and universe pale in comparison. That is why the follower of Jesus has joy. His or her comfort and solace is in this God. The humble are always joyful, even when they are sad. A joyful person believes in the good news of Jesus and trusts that He will accomplish all that He has promised. They are aware that they cannot take joy in themselves because they are weak, fallible, and fickle. Only God can save them, He is their only hope. They cannot trust in their works to save them. They cannot trust in their upbringing. Neither can they trust in their good nature because it is a filthy rag to a righteous God (Isaiah 64:6). Men "alone" in their presumption think they are good, but they don't know what good is until they get a glimpse of the Eternal God laid out in Scripture. They also find that it is He alone who gives sight to the blind, hearing to the deaf, and raises the dead. God resists the proud but gives grace to the humble (James 4:6). Why? The humble have faith, and that faith is a gift so that no man may boast and be proud (Ephesians 2:8). They cannot take credit for their efforts, but they can only give God the glory. He "alone" is worthy. The humble take joy in that. So no matter whether they are rich or poor, hungry or full, they are content with God and believe that they can endure all things this world throws at them because their joy is rooted in such a sturdy source (Philippians 4:11-13) It is only when we totally trust and lean on this God (faith) that we can "do good" and for Him to be pleased with anything that we accomplish (Hebrews 11). Faith wrought works done in the Spirit of joy is pleasing to God. Self-righteous works done in the pleasure of self and worldly ambition are filthy and no good. Can you see the difference? We should test the spirits and examine ourselves today to see where we stand (1 John 4:1/ 2 Corinthians 13:5). Do you totally depend upon God? Is He your only hope? If so, you have the right demeanor. May God be glorified as we tread upon this wasteland, this ship heading for certain destruction while we warn the passengers of the future so that they may hope, have joy in, and cling to the only One who can rescue them from this certain doom.