All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
The truth about the existence of the human being is that he is the slave of Allah, The Exalted, Who created him from nothingness, sustained him, showered him with blessings and bounties, and commanded him to worship Him alone with no other partners, and promised him Paradise were he to obey Him or Hellfire were he to disobey Him. Allah, The Exalted, says (what means): {O mankind, worship your Lord, Who created you and those before you, that you may become righteous.} [Quran 2:21]
So if this human being is too arrogant to worship His Creator under the pretext of personal freedom of choice, he has wronged himself and abused the concept of freedom. Verily, worshiping Allah, The Exalted, alone is the true freedom. Moreover, the person who has a sound disposition is bashful of violating the command of the one who showed him kindness. If another human being showed kindness towards your friend, providing him with food, drink, clothing, accommodation, college tuition, and medication, and then asked him for something simple and easy for him to do, he would feel embarrassed to not fulfill his request given the good that that person had done to him, and he would perceive himself neglectful if he does not fulfill his request while that kind person is a created being just like him. How, then, should he react when the One asking him is the Almighty Creator, Who has created him and granted him all the blessings and bounties that he has enjoyed ever since he was a helpless fetus inside his mother's womb?! Nevertheless, he refuses to worship Him, obey Him, and thank Him, and believes that he is free to not fulfill His command. Rather, he worships other than Him and disbelieves in his Creator and Sustainer! Allah, The Exalted, says (what means): {Cursed is man; how disbelieving is he.} [Quran 80:17]
And He says (what means): {And He gave you from all you asked of Him. And if you should count the favor of Allah, you could not enumerate them. Indeed, mankind is (generally) most unjust and ungrateful.} [Quran 14:34]
Al-Baghawi commented on the verse, saying, “It means that such a person wrongs himself by committing sins and being ungrateful to his Lord, Who bestows bounties and blessings upon him. It is also said that the verse refers to the person who is given to injustice and thanks other than the one who bestows the blessings upon him. The word Kaafir (disbeliever) in Arabic denotes being ungrateful towards the one who bestows upon him blessings...”
So, we advise you, dear Brother, to strive in calling this young man to Islam and convince him that he is a slave to Allah, Who created him and governs his affairs, and that his understanding of freedom is incorrect. You should explain to him that Allah, The Exalted, wants him to be genuinely free from servitude to anyone and anything but Him. He sent him Messengers and Divine Books to guide him to the truth; he has no excuse to meet His Creator and Lord on the Day of Judgment following any other religion but the one He chose for him, which is Islam.
Allah knows best.