In the beginning, we were created in a state of original innocence and given free will (the ability to choose to do the will of God, that which is truly good).
When the Evil One tempted our forefathers, he presented an evil with the appearance of good in order to lead us into disobedience (a choice contrary to God’s will). That is sin. Its motto is I will not serve God and neighbor. The result: a turning inwards in a selfish motion that bends us on our root vices (desire for power, desire for pleasure, desire for wealth) and eventually into the idolatry of self (“you will become like God”, said Satan). Which is why we are called to conversion, literally, turning towards God - a Father that loves us unconditionally.
In the Garden, our forefathers hid in their shame because of their sin. They turned away from God, literally. But “where can I hide from the Most High”? And God went out to meet them in their sinful state, calling them into His holy presence. Indeed He is the One who “comes to seek not the righteous but the sinner to repentance”. To the righteous He says: “all that is mine is yours”. But to the sinner, He opens the fount of mercy so that the hope of conversion becomes a reality in their soul by a very special, gratuitous grace that moves the soul to repentance. Hence the “walking with God” (life of faith) and the awareness that God is love (1 Jn) and that is why, in the end of time, faith and hope shall pass, but love shall remain.
Aquinas explains that every object of temptation has in the eye of the tempted the appearance of good. But true good is only that which is in accordance with God’s will for us. What is good for me may be an evil for another. Which is why Ignatius of Loyola teaches us that discernment of spirits does not involve good versus evil, but two “goods”, one of which only apparently good because presented as such by the spirit against Christ.
The eternal law is God’s will, inscribed in the human soul. Contemplation leads us to the perfection of discipleship. Mary was born in original innocence and preserved it. Like Eve, she was capable of sinning, but she never did. Many saints have faced the hard struggle of the “way of perfection” and realized that it is only with time and patience, prayer and interior silence, that we form our conscience and become “attuned” with the voice of God. Then our will, as it were, vanishes inside God’s will, much like the human will of our Savior perfectly cooperated with His Divine Will.
The Commandments are a good beginning.
Also: “Love God with all your heart and your neighbor like yourself”.
Also: “Love one another as [Christ] has loved you.”
Also: “Whatever you do to the least of your brothers, you do it to [Christ]” (whether it is good or bad).
In the West we have a very legalistic mindset. We want clearly defined rules. The economy of salvation is mysterious. Mercy and Justice are not easy to comprehend, because “God’s thoughts are not our thoughts and God’s foolishness is greater than man’s wisdom”.