It means human beings unity and equality in their relation with God almighty. He is the God of all people with no exceptions. No one has a special relation with Him because of his human nature. No one has family bonds with Him. He is neither the God of a specific nation or tribe nor He chose a specific nation to lead and others to be servants. All people are equal in God’s eyes, and no one is distinguished except in his good deeds through striving for people’s needs and performing God’s principles that lead a man to reach highness.
God almighty says:” They say, “Allah has offspring.” Glory be to Him! In fact, to Him belongs whatever is in the heavens and the earth—all are subject to His Will”
“So whoever does good and is a believer will never be denied ?the reward for? their striving, for We are recording it all” 
“O humanity! Indeed, We created you from a male and a female, and made you into peoples and tribes so that you may ?get to? know one another. Surely the most noble of you in the sight of Allah is the most righteous among you” 
It also means the unity of human beings and equality in creation and human formalization. Humanity is a common factor which is equally present in all humankind. They are not many deities that created many humankinfs. Therefore, there are not many strong differences in creation. Same as the God of the high social class isn’t stronger than the God of the lower social class. All people are the creatures of the one and only God and they are all common in the essence of their creation. “O humanity! Be mindful of your Lord Who created you from a single soul” 
It also means the equality of human beings in the abilities they are provided with to reach distinction and perfection. People are similar in their human kind and essence. This nature was framed by a wise creator. Then, there is no self preventer from moving towards the straight path to reach distinction and perfection. Starting from here, God’s call is a general call. It is not limited to a specific or special nation. Different circumstances have their impacts on a man, but these urgent conditions weren’t able to make a human being with full devil or angel characteristics, tie his hands, take his choice, and prevent him from changing.
God almighty says:” We have sent you ?O Prophet? only to all of humanity” 
“We have sent you ?O Prophet? as a messenger to ?all? people”
“O humanity! There has come to you conclusive evidence from your Lord. And We have sent down to you a brilliant light. As for those who believe in Allah and hold fast to Him, He will admit them into His mercy and grace and guide them to Himself through the Straight Path” 
It also means the freedom of all people from the chain of captivity and the servitude of people other than God. It is another expression for the importance of servitude to God because those humans who are subjected to an intellectual, cultural, economic or political control, are slaves for other people according to the wide definition of worship. Those people consider some people as peers for God almighty. Atheism rejects such a lifestyle. It considers a human being a slave for God only and frees him from subjection to any servitude for every regime or prevailing factor that puts itself in God’s almighty place.
Atheism means to only resign oneself to the will of God almighty. This is followed by rejecting every authority other than that of God whatever its kind or type is. “It is only Allah Who decides. He has commanded that you worship none but Him” “For your Lord has decreed that you worship none but Him”
The updated definition of atheism means honoring a human being and appreciating him. An honorable human factor is higher than being subjected to someone other than God. The immortal existence and beauty only appreciate being worshiped, praised, and admired by a human being. This honorable desire is one of the ranks of honor.
Nothing other than God almighty has the dignity which deserves a man’s worship and supplication. All concrete and movable idols that obligatory imposed themselves on a man’s mind and body and violate God’s authority in a man’s life are considered an enormity that moves a human being away from his instinct purity. They humiliate him and prevent him from moving on. Then, if a man wants to get back his distinctive dignity, he should be away from these idols and purify his life from the dirtiness of their servitude, “So shun the impurity of idolatry, and shun words of falsehood. Be upright ?in devotion? to Allah, associating none with Him ?in worship?. For whoever associates ?others? with Allah is like someone who has fallen from the sky and is either snatched away by birds or swept by the wind to a remote place” , “Do not set up any other god with Allah, or you will end up condemned, abandoned” , “And do not set up any other god with Allah ?O humanity?, or you will be cast into Hell, blameworthy, rejected”.
It also means the unity and conformity between a man’s life and existence. They are composed of intellect and reality, thinking and working. So if one of these parts is partially or totally subjected to God’s enemies, the double standard of a man’s life will be present with polytheism. This happens when a man is characterized with a divine mind with an opposite reality, or when he has a divine reality but an opposite mind which is far away from God.
In this case, a man looks like a magnetic indicator that faces a foreign body. So the indicator will either totally deviate from its normal direction or remain moving right and left. This means that a man will deviate from the straight path that suits his human nature, so he will deviate from God almighty. “Do you believe in some of the Scripture and reject the rest? Is there any reward for those who do so among you other than disgrace in this worldly life and being subjected to the harshest punishment on the Day of Judgment” 
It also means a man’s conformity with his surroundings. The universal wide space is full of divine laws where no single phenomenon is out of the frame of these laws. Through the conformity and collaboration of these laws, the universe is managed and this wonderful system is spread in the world. A man is a part of this group. It is controlled by these general and specific laws. However, these specific laws are comfortable and convenient with other phenomenon laws.
However, a man, in contrast to other phenomena which are subjected to move according to his natural instinct, because this is the path of his distinction and perfection. This means that he’s able to deviate from his normal way, “Whoever wills let them believe, and whoever wills let them disbelieve.”
Atheism calls a man to walk on his instinct and normal path which is compatible with all the universe. By that, a human being, who is considered an original organ of this universe, is connected by his work and efforts with all the universe parts to create complete unity and conformity. “Do they desire a way other than Allah’s—knowing that all those in the heavens and the earth submit to His Will, willingly or unwillingly, and to Him they will ?all? be returned?”, “Do you not see that to Allah bow down ?in submission?1 all those in the heavens and all those on the earth, as well as the sun, the moon, the stars, the mountains, the trees, and ?all? living beings, as well as many humans” 
Soul of Atheism (Rejection of Slavery for Other than God), Al Imam Al Khomeini (may God protect him)- Freely
 Surah Al Baqarah verse 116
 Surah Al Anbiya’ verse 94
 Surah Al Hujurat verse 13
 Surah Al Nisa’ verse 1
 Surah Saba’ verse 28
 Surah Al Nisa’ verse 79
 Surah Al Nisa’ verses 174-175
 Surah Yusuf verse 40
 Surah Al Isra’ verse 40
 Surah Al Hajj verses 30-31
 Surah Al Isra’ verse 22
 Surah Al Isra’ verse 39
 Surah Al Baqarah verse 85
 Surah Al Kahf verse 29
 Surah Al Imran verse 83
 Surah Al Hajj verse 18