Faith

God's commandments are divided into two sections. The first five address the 'vertical' relationship between ourselves and God (and our parents). The second five address our 'horizontal' relationships with our fellow man. The first five are summed up in the commandment 'Love God', and the second five are summed up in the commandment 'Love your neighbor'.
When God gave His one commandment to Adam and Eve in the Garden of Eden, it represented the first five laws of Moses. The forbidden fruit represented the question of whether or not Adam and Eve were willing to love and worship God. It represented the question of whether or not they were willing to acknowledge:

1. The infinite wisdom of God.
2. The righteousness and trustworthiness of God.
3. The goodness, kindness and generosity of God.
4. The infinite power of God.
   
   OK, so faith was the right attitude toward God, and a fulfillment of the first five laws of Moses. But what about Adam's everyday interactions with other people? What would define a righteous approach to his fellow man? God's plan was simple. As Adam supplied the 'primary righteousness' of believing and honoring God, not eating the forbidden Fruit, God was going to enter Adam's body through the Holy Spirit and live inside him. The love, kindness, goodness and compassion of God Himself would flow out of Adam's heart. This is still God's plan today. God wants to share His very nature with us; He wants us to truly know what it is like to be God.
   "Not by might, nor by power, but by My Spirit" says the Lord of hosts.
   Zechariah 4:6
   For as many as are led by the Spirit of God, they are sons of God.
   Romans 8:14
   But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, gentleness, self-control. Against such there is no law.
   Galatians 5:22-23
   Wherefore, my beloved, as you have always obeyed, not as in my presence only, but now much more in my absence, work out your own salvation with fear and trembling; for it is God who works in you both to will and to do of His good pleasure.
   Philippians 2:12-13
   To whom God would make known what are the riches of the glory of this mystery among the Gentiles: which is Christ in you, the hope of glory.
   Colossians 1:27
   Whereby are given unto us exceeding great and precious promises: that by these you might be partakers of the divine nature, having escaped the corruption that is in the world through lust.
   2 Peter 1:4
   
   Righteousness belongs to God alone. It is a supernatural trait. For instance, the ability to love our enemies is supernatural; we are not capable of it. But we can experience this 'secondary' righteousness if we are willing to provide the 'primary' righteousness of acknowledging and glorifying God.
   As I have just pointed out, the forbidden Tree represented the most important Law of all time:
   You shall love the Lord your God with all your heart, and with all your soul, and with all your might.
   Deuteronomy 6:5, Matthew 22:37
   In requiring that Adam and Eve simply believe Himself, God was asking them to acknowledge His glory and trustworthiness, while also being thankful that He had created them and had given them all that they had. It was a most reasonable request and commandment.
   Faith is often referred to in the Bible as 'godliness'. It is an acknowledgement of God's glory, and of the worship that He deserves. A proper attitude toward God is also the foundation of all other righteousness. When our hearts are right toward God, they are 'tuned' to relate properly with our fellow man as well. It is impossible to love our fellow man if we do not love God first. The logic of this is straightforward.
   Suppose a thief commits murder during a bank robbery, killing a bank employee. Do you suppose that he will be concerned about running stop signs during his getaway? Of course not. If he has committed the greater crime, he will have no regard for lesser laws. The same thing applies to mankind. If we are willing to ignore our Creator, and even to declare war against Him, how can we love lesser beings who are mere creations? It is impossible to truly value or respect a fellow human being, if we are unwilling to love God. The apostle Paul explained how all of man's wickedness toward our fellow man flows out of the first and greater crime of disrespect for God:
   And even as they did not like to retain God in their knowledge, God gave them over to a debased mind, to do those things which are not fitting; being filled with all unrighteousness, sexual immorality, wickedness, covetousness, maliciousness; full of envy, murder, strife, deceit, evil-mindedness; they are whisperers, backbiters, haters of God, violent, proud, boasters, inventors of evil things, disobedient to parents, undiscerning, untrustworthy, unloving, unforgiving, unmerciful; who, knowing the righteous judgment of God, that those who practice such things are deserving of death, not only do the same but also approve of those who practice them.
   Romans 1:28-32
   King David also recognized this connection between how we treat God, and how we treat our fellow man, confessing that his adultery and murder had their roots in his opposition to God:
   Against You (God), You only, have I sinned and done this evil in Your sight.
   Psalm 51:4

This connection, between faith in God and obedience to God's entire Law, is seen in God's two-part description of Abraham's character. First God acknowledged the righteousness of Abraham's faith, and then acknowledged Abraham's fulfillment of all of His laws:
Abraham believed in the Lord, and He counted it to him for righteousness.
Genesis 15:6
Abraham obeyed My voice, and kept My charge, My commandments, My statutes and My laws.
Genesis 26:5
The apostle Peter also pointed to the 'heart-purifying' nature of faith. In explaining to his fellow Jews why he declared the gospel of Jesus Christ to 'unclean Gentiles', Peter said...
So God, who knows the heart, acknowledged them (the Gentiles) by giving them the Holy Spirit, just as He did to us (Jews); and made no distinction between us and them, purifying their hearts by faith.
Acts 15:8-9
Faith (believing God) represents obedience to the first and greatest commandment. And where genuine faith is found, love for our fellow man and fulfillment of the rest of God's commandments will surely follow. This connection between faith and obedience is also found in the book of Revelation, where believing the Gospel and keeping God's commandments go hand in hand:
And the dragon (Satan) was angry with the woman (Israel), and went to make war with the remnant of her seed (Christians), which keep the commandments of God and have the testimony of Jesus Christ.
Revelation 12:17
Here is the patience of the saints: here are they that keep the commandments of God and the faith of Jesus.
Revelation 14:12