HaShem created each and every one of us, handmade us, formed us and bestows upon us countless blessings every single day of our lives. He desires for us to serve Him and only Him, to call upon Him and to recognize Him as the Source of everything.
One of the most heinous of crimes is idolatry, one of three sins which Jews (and non-Jews) must give their lives rather than transgress. What is idolatry? Idolatry is the worship of anything other than HaShem, imposing a limit upon Him or giving Him a form. HaShem has neither body, nor form. He is transcendent and non-physical. HaShem is beyond physical limitations, above the world, unbound by time and space. HaShem is One, an absolute unity, since more-than-oneness is a feature of physicality, which He is not limited to. “HaShem, He is G-d ― there is none else beside Him” (Deuteronomy 4:35). Everything is dependent upon Him, the Ruler of All, and nothing can has any power or divinity other than HaShem. We can then say that God is both omnipresent and transcendental, two words that express the idea that God is not in space-time. Omnipresent means He fills the entire universe, as Isaiah the prophet states in Prophets, “Holy, holy, holy is G-d of hosts -- the whole world is filled with His Glory” (Isaiah 6:3). Since the entire earth is filled with His glory, HaShem cannot have a shape as that would constrict Him. Time and time again, He forbids us form making idols of silver or gold, or giving Him any shape. “Take good heed of yourselves, for you saw no manner of form on that day when G-d spoke to you at Horeb...” (Deuteronomy 4:15)
HaShem rules the world according to His will and as the Plagues of Egypt and the Exodus demonstrated, HaShem manipulates the forces of nature as He pleases. No one can oppose or be contrary to His desire. The ancient pagans resolved the question of theodicy by claiming that there was a good god and a bad god, in constant struggle. All harsh or seemingly evil things come from the bad god while all good things come from the good god. This dualism still exists in certain beliefs in a Satan, Opponent of G-d, Prince of Evil, who tries to frustrate G-d's plans. This is idolatry since it attributes independent power to something other than HaShem. "I form the light, and create darkness; I make peace, and create evil; I am the LORD, that doeth all these things." (Isaiah 45:6). Everything that befalls you, sweet or harsh, is decreed directly from G-d, the Lord who dictates good and evil. There is none other!
Maimonides explained in his “Laws of the Worship of Stars” how idolatry came about in the first place: “In the days of Enosh, mankind made a great mistake... seeing that G-d had created the stars and constellations... and set them in the sky and gave them a place of honor... they assumed that these were worthy of praise... They began to build monuments and offer sacrifices, to verbally extol them and bow down to them.” The people of Antiquity held that they were ruled by stars and constellations, that they each had a destiny decreed for them according to their Zodiac sign. Many peoples had a belief in a single transcendent G-d who created the world but that He was too far removed from the world so they worshipped His messengers ie. angels, nature, planetary influence. They failed to understand that although HaShem is "the G-d of gods, and Lord of lords, the great God, the mighty, and the awful, who regardeth not persons, nor taketh reward" (Deut. 10:17), He takes interest in the deeds of man and is actively involved in the ruling of the world. At Mount Sinai, G-d's first command was "I am the LORD thy God, who brought thee out of the land of Egypt, out of the house of bondage." (Exodus 20:2) Why did G-d associate Himself with the Exodus rather than the Creation of the world since the latter was certainly more lofty? Because no man saw the creation but millions witnessed the Exodus, as testimony to G-d's involvement in the world. As refutation to those who believe that G-d directs big things like the rise and fall of nations but doesn't concern Himself with the lowly deeds of individual men, the verse states that G-d not only took the entire nation of Israel out of Egypt but each individual family out of their own personal "house of bondage".
Despite G-d's Abssolute "Unknowable-ness", that He is Ein Sof, limitless, He is not unreachable. G-d is accessible to everyone who sincerely calls upon Him in prayer. The Torah forbids the use of an intercessor, stating "Thou shalt have no other gods before Me." (Exodus 20:2), before Me ie. as an intercessor. Praying to a demigod or something else to reach G-d is blasphemous and idolatrous. There is nothing else worth our prayers and devotion other than HaShem, Everlasting G-d. The only power or divinity is HaShem and no man, angel, star, creature or force of nature has any power besides Him. Since G-d is Omnipotent and calls upon us to pray to Him directly, why waste time directing prayers to anyone other than the Ribono shel Olam, Master of the World?
"Know this day, and lay it to thy heart, that HaShem, He is G-d in heaven above and upon the earth beneath; there is none else."
There is none else!