The first of the Ten Commandments is, “I am the Lord [literally, the Y-H-V-H four-letter holy Name, which we protectively refer to as HaShem, The Name] your God who brought you forth from the land of Egypt.” The second command is “You shall have no other gods beside Me.”
Rabbi Moshe Feinstein tells us that the first command is not just a command to believe in God. The first command tells us that we believe in God, and if we believe in God, we must pray to Him. We must treat Him like a God, in worship, in prayer, having faith in Him, etc.
Thus, the first command centers on a belief in God; from this flows our need to relate to Him as our Creator and sustainer. Inherent in this relationship is prayer, faith, obedience, etc.
The Second command, about paganism, begins with the First Command. A person believes in God. So why must we tell him not to worship idols? The answer is that people can believe in God and still want to worship idols. Why is this?
A person who believes in God may be so much in awe of God that he needs an intermediary. This is paganism, but it is not a paganism that rejects the First Command. It is a paganism as a reaction to the First Command. One who trembles before the Eternal may want an intermediary to make it easier to relate to Him. Also, a person may decide that he cannot relate to an invisible deity, and he wants an idol.
Thus, the Second Command is a continuation of the First Command. We must worship God, and we must worship Him with all of His transcendence. This is not easy. Indeed, how is it done?
Just as an adult parent coos and kutchies a baby, so does the Perfect God, our Father, love all of us. When we recognize this, we gain the courage to relate to God without an intermediary.
A religion that despises people, on the other hand, may need an intermediary, because a lowly, sinful human may feel inadequate to deal directly with God.
Judaism teaches how beloved all creatures are to God. From this flows the ability to reject paganism, and to embrace God.
Every second that we think about God, our soul connects to heaven and holiness flows into it. Every second that we have faith in God, the same happens. Our life is an endless opportunity to gain more and more mitsvose and commands by just believing in God. Not only is just believing a great mitzvah, but it is the mitzvah from which everything else flows.
The Psalmist (64:11) says, “The righteous will rejoice in God, and trust in Him; and all people of honest heart will be praised.” The righteous not only believes in God, but connects with Him. As the Presence comes near, and heavenly holiness flows into his soul, the righteous person rejoices; he senses a divine protection and security. Thus, “The righteous will rejoice in God, and trust in him.”
Those who achieve the high level of being of “honest heart,” one so close to God that no crooked thought enters his heart, merit such closeness to heaven that they are “praised” and truly elevated.
Our heavenly judgment will be about our beliefs, perhaps even more than about our deeds. All deeds, all thoughts, words and actions, flow from our beliefs.
But ultimately, our belief that God is One requires action. We must spread this knowledge to the world so that, “And it will be when God is King of all of the world, on that day, God will be One and His Name One.”
A remarkably profound article on the future completion of the Name of God, which goes to the heart of the famous Kaddish service [the so-called Jewish "prayer for the dead"] and helps explain it, can be read here - Eternal Life/Soul of Fire (a Deep Look Into the Beyond)- or here: Ethan Dor-Shov.