"...to set up partners with Allah is to devise a sin most heinous indeed."
(Qur'an: Translation of the meaning, 4:48)

"And when Luqman said to his son while advising him: "O my son! Do not ascribe partners to Allah. Indeed shirk is a great injustice."
(Qur'an: Translation of the meaning, 31:13)

An injustice is to withhold someone's rights or to treat someone in an unjust manner. Making a companion with Allah Almighty is thus the greatest injustice. Man considers an entity which has no power whatsoever to control his life, to be equal to his creator, sustainer and savior. In praising and worshipping these imaginary deities, he forgets Allah's sole right to be worshipped. He uses his health, his facilities, all his material earnings and all the amenities that are at his disposal to pray to others. He thus ignores the Creator Who has given him the air to breathe, the health to use, the environment to utilize and the wealth to enjoy. He forgets that he is indebted to one Being only for everything that he has, the most important of which is his life, and turns to false gods in reverence. He is ungrateful and unjust to his Benevolent and Merciful Creator. Shirk is an unforgivable sin.

"Indeed Allah does not forgive joining other gods with Him but He forgives other sins than this of whom He pleases. And the one who joins other gods with Allah, indeed he has strayed very for away."
(Qur'an: Translation of the meaning, 4:116)

"Indeed they do blaspheme who say that Allah is Christ the son of Mary. But Christ said: "O Children of Israel! Worship Allah, my Lord and your Lord. "Whoever joins other gods with Allah -- Allah will forbid him Heaven, and the Fire will be his abode. And there will be no-one to help the wrong-doers."
(Qur'an: Translation of the meaning, 5:72)

"And it was revealed to you (O Muhammad) and to all (the Prophets) before you that if you commit shirk, all your good actions will be wasted and you will be one of the losers."
(Qur'an: Translation of the meaning, 39:65)

Therefore, none of the deeds of a person who makes a companion with Allah Almighty will be regarded as good, none will earn reward for him, and his whole life will have been a waste.