Idolatry

Sin isn’t only doing bad things, it is more fundamentally making good things into ultimate things. Sin is building your life and meaning on anything, even a very good thing, more than on God. Whatever we build our life on will drive us and enslave us. Sin is primarily idolatry.
Tim Keller

All those who do not at all times trust God and do not in all their works or sufferings, life and death, trust in His favor, grace and good-will, but seek His favor in other things or in themselves, do not keep this [First] Commandment, and practice real idolatry, even if they were to do the works of all the other Commandments, and in addition had all the prayers, obedience, patience, and chastity of all the saints combined. For the chief work is not present, without which all the others are nothing but mere sham, show and pretense, with nothing back of them... If we doubt or do not believe that God is gracious to us and is pleased with us, or if we presumptuously expect to please Him only through and after our works, then it is all pure deception, outwardly honoring God, but inwardly setting up self as a false [savior]...
Martin Luther from "A Treaties on Good Works"

Because we are, each of us, the image of God, we will worship, in fact we must worship, someone or something, either our original, as we should, or, with the illusion that we are the original or our own ultimate point of reference, ourselves. If the latter, we will give ourselves over, with the full, still efficient resources of our imaging capacities, to some figment, some distorted image, focused on ourselves or on some aspect of the world, ultimately seen as an extension of ourselves. What Calvin observed long ago is no less true today: the human heart, our image-bearing and image-fashioning nature, is an idol factory.
Richard Gaffin from "Speech and the Image of God" in The Pattern of Sound Doctrine