We're told (somewhere in the NT) that nature and the world around us speaks to the existence and nature of God. But, we, as humans, largely chose to exchange the truth for a lie and we worshiped/worship idols of our own making (modern secular ideas, paganism, false versions of Christianity, etc.).
Its worth noting that the Bible also tells us that God will blind us to His existence and keep us from repentance. He did it to Pharaoh when the plagues were hitting Egypt, and we're told in the NT that its possible for our conscience to become so seared by sin that we become hardened, incapable of recognizing God, much less of turning to Him.
As a baby Calvinist, the way I've worked it out in my mind (I hope this is scriptural) is this: we're born sinful. Without divine intervention, we get ever more sinful. We have a (sinful) tendency to worship Gods and Ideas of our own making, and we suffer for this. If we're part of the Elect, God will at some point soften us up to His Word (regeneration) and then save us from sin, Satan, and Death (salvation).