As Christ says in his prayer in John 17, Eternal Life is knowing God. Solomon states in Ecclesiastes 3:11 that God has set eternity in mankind's heart. Essentially, God has put the knowledge of himself in all creatures, so that we might grope for him and discover him in this life. However, all men and women, to various degrees, bury him in the conscience, piling over top of God idol after idol as a substitute. As we read in Romans 1, we suppress the truth in unrighteousness, because even with all the evidence in creation, we do not seek God. We tend to seek only our own pleasures and self worth. Some merely don't seek him, while others actively hate him. Either way, not honoring God or giving thanks to him for life, we devolve into futile speculations about the nature of things. We are fools and worship the creature, because men and animals are manageable. God himself is so vastly superior and awe-inspiring that it would crush us to nothing to acknowledge his glory. Such are all of us, but some travel far down the path of unrighteousness, whereas God has snatched others out of such futile thinking, as if brands from a fire. He has saved some.
The unsaved continue down the path far, burying God beneath so much idolatry and self-conceit, that they do not even believe that a God exists. Psalm 14:1 reads, "the fool has said in his heart, 'there is no God.' " Although the ungodly one does not fear God, he makes an idol of his own sin, and he elevates himself as God. God allows the unrighteous to pursue this course, and as a result, they never linger around the cusp of belief. They sprint toward deeper and deeper depravities until they cannot return to possible redemption, it seems. Jesus himself tells his disciples that this is the reason he speaks in parables. Those who are on the cusp of belief will understand the parables, being nudged in the right direction by the Holy Spirit. Those who have cast themselves away from God's grace cannot hear the meaning of the parables, and they sound like nonsense and foolishness to them.
All of this is best summarized in the words of Psalm 36:
Transgression speaks to the ungodly within his heart;
There is no fear of God before his eyes.
For it flatters him in his own eyes
Concerning the discovery of his iniquity and the hatred of it.
The words of his mouth are wickedness and deceit;
He has ceased to be wise and to do good.
He plans wickedness upon his bed;
He sets himself on a path that is not good;
He does not despise evil.
Your lovingkindness, O Lord, extends to the heavens,
Your faithfulness reaches to the skies.
Your righteousness is like the mountains of God;
Your judgments are like a great deep.
O Lord, You preserve man and beast.
How precious is Your lovingkindness, O God!
And the children of men take refuge in the shadow of Your wings.
They drink their fill of the abundance of Your house;
And You give them to drink of the river of Your delights.
For with You is the fountain of life;
In Your light we see light.
O continue Your lovingkindness to those who know You,
And Your righteousness to the upright in heart.
Let not the foot of pride come upon me,
And let not the hand of the wicked drive me away.
There the doers of iniquity have fallen;
They have been thrust down and cannot rise.
Even then, all is not lost. God can take the most vile of sinners and breathe life into him. The reason is, in actuality, only Christ is saved, because he is sinless. He is the one with whom the covenant between God and Man was made, and so his righteousness saves him. We, however, can be saved by faith alone. Just an ounce of faith--a mustard seed--can move mountains and can also move a man from the brink of everlasting destruction into Christ, our salvation, our ark. Faith is all one needs, and with this faith, the Holy Spirit cleanses us to prepare us for everlasting life. Our sins are removed, crucified with Christ on the cross, and his righteousness is reckoned to us. Christ is saved, and we are saved with him, as long as we are in him by faith.