in the Middle Ages, which preceded the Renaissance, everything was basically centered around God, and life was arrayed according to the “Great Chain of Being,” which was the hierarchy by which all things were organized in God’s view.
With the introduction of Classical texts by Greco-Roman authors, there came a new consciousness in the value of the human, hence the name “humanist.” Authors like Petrarch started writing about themselves, rather than God, turning inward through the use of poetry to express the human condition. The philosopher Pico della Mirandola wrote An Oration on the Dignity of Man which, contrary to the dominant Christian view at the time, attributed to humans absolute free will, arguing that we have the power to shape ourselves according to our wills, rather than by God. Artists did not stop painting Christian themes, but they did paint more every day images depicting landscapes with proper proportions and human figures from Classical times, showing a departure from the religious-dominated art world.
In short, the Renaissance differed from “the way most people thought before” by turning away from God and toward humans.