How entirely different are the two purposes that exist in life: The first, to glorify God; and the second, to glorify self. The two reasons to exist can be so readily confused in the human mind, and people can be so oblivious or indifferent to the idea that there is something other than glorifying self.
The Bible makes it abundantly clear that the default tendency of humanity is to love self, take care of self, and glorify self. Even when we think we are being selfless, often it is for selfish motives: to make self look or feel good, to gain affection and acclaim for self.
Considering all the various religions that exist whose believers do not know God, but often think they do, it's tragic to consider that everything that those people do is a sham. The Bible is clear that "...without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him." If we don't believe in the true God, we are incapable of pleasing Him, and everything we do is fruitless, pointless, eternally and spiritually empty. Not only that, but if we do believe in Him, even if our theology is right, if we are in the wrong frame of mind and spirit, then we are doing the same as the unbeliever.
Think of the seemingly good work that is done in the wrong motivations: hospitals, heroic acts, donations, programs, missions work for the wrong purpose. All these sacrifices of time, money, talent, body parts, even lives...all gaining only momentary results and only pleasing self and Satan.
I believe that even doing what would be God's work for the wrong motives is the same as all the rest: even pastoring a church; even working as a missionary; even witnessing to a neighbor. If we don't do it through the power of the Holy Spirit, if we do it in our own strength, in our own judgment, then it means the same as the work of an unbeliever. I do believe also that God can use it for good, just like He can use anything for good; just as Joseph's brothers sold him into slavery for good. But work done without the Holy Spirit's leading isn't done in His power and timing, and I think it doesn't knit so perfectly into His plan or at least it doesn't please Him. It will not be likely to bring the amazing fruit as when it's done by walking in the Spirit. The worker working in his own strength doesn't build on the Church's foundation with anything but wood, hay and stubble (1 Cor 3:10-15), which will be burned at the end.
Galatians 5:16-21 So I say, live by the Spirit, and you will not gratify the desires of the sinful nature. For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want. But if you are led by the Spirit, you are not under law. The acts of the sinful nature are obvious: sexual immorality, impurity and debauchery; idolatry and witchcraft; hatred, discord, jealousy, fits of rage, selfish ambition, dissensions, factions and envy; drunkenness, orgies, and the like. I warn you, as I did before, that those who live like this will not inherit the kingdom of God.
The amazing thing to me about this verse is that it lists such a wide range of sins, including selfish ambition alongside the likes of witchcraft. Still, since I am conscious of this, you would think that I would be as fully committed to walking in truth as anyone, and yet I find myself being stupidly selfish a shocking amount of the time. I don't take every thought captive; I do things for the sake of being seen; I hope for approval of men; I am selfish in the utmost. I know it; I'm inside of me and have caught myself when no one else might suspect. Maybe Paul had some of the same trouble, though I know from reading his writings that he spent more time doing extreme things for God at complete risk of self than anyone I've even read about other than Jesus.
Paul wrote the following: Romans 7:18-25: For I know that nothing good dwells in me, that is, in my flesh; for the willing is present in me, but the doing of the good is not. For the good that I want, I do not do, but I practice the very evil that I do not want. But if I am doing the very thing I do not want, I am no longer the one doing it, but sin which dwells in me. I find then the principle that evil is present in me, the one who wants to do good.
For I joyfully concur with the law of God in the inner man, but I see a different law in the members of my body, waging war against the law of my mind and making me a prisoner of the law of sin which is in my members. Wretched man that I am! Who will set me free from the body of this death? Thanks be to God through Jesus Christ our Lord! So then, on the one hand I myself with my mind am serving the law of God, but on the other, with my flesh the law of sin.
Why is it that I receive comfort from the idea that Paul battled sin too, the idea that misery loves company? Well, Paul doesn't offer only that for my comfort, but something much better: the freedom and hope that comes in knowing Jesus Christ. Jesus will set me free from this body of death, and I praise Him for that. Hallelujah! What a Savior!