Very much condensed version.
The concept of deities that are essentially human in nature, but bigger and supernaturally powerful, dates way back before Judaism. Many ancient religions were pantheistic - a belief that many gods existed. Some believed in one supreme high god that ruled over the others (a Zeus or Wotan) but not all did. Some, like Hinduism, developed the concept that their pantheon of gods actually were different aspects, or faces, of three supreme gods, and that even these three were the basic three faces of THE supreme, unknowable being.
Somewhere around the time that the Hebrews departed Egypt (however close the Biblical accounting is or is not), the belief in a particular sky/storm god named Yahweh became prevalent with the Hebrews. But the Hebrews did not believe Yahweh to be THE one and only true god. They did, in fact, believe that other gods existed (such as Baal). Yahweh may actually be rooted in an even more ancient pantheon of gods out of Sumerian or Chaldean/Babylonian belief.
In any case, what the Hebrews believed was that Yahweh was the only god that should be worshipped, and that all other gods really existed but were evil, or subordinate to Yahweh, etc. They were "henotheistic" - a sort of in-between pantheistic and monotheistic. A belief that many gods existed, but only one was right to be worshipped.
Worship of Yahweh helped motivate the Hebrews to try to reclaim lands in what is modern day Israel. It also grew into the belief that Yahweh was the same god that their claimed Canaanite ancestors (Abraham, Isaac, Jacob) had worshipped. That may or may not be the case. But also, it grew into the belief that the Hebrews were Yahweh's "chosen people", and that as chosen people they were destined to be rewarded with supreme, earthly power one day. It also meant that any time the Hebrews faltered or stumbled in power, when Jerusalem was taken by a neighboring power or the Hebrews suffered terrible battle loss, they viewed that as their failure to worship Yahweh properly, and thus Yahweh was using these other nations and people to specifically punish the Hebrews. Only when they returned to covenant with Yahweh did Yahweh again bless his chosen people.
However, it is clear in the first few books of the Bible that there is a very different god involved as well. These parts of Genesis, for example, are said to be written by the "Elohist" author (as opposed to other parts written by the "Yahwist" author). This author named God as "El" or "Elohim" and in fact this word appears still in traditional Hebrew prayers. Whereas Yahweh is identifiable as a "sky/storm god", similar perhaps to Zeus or Thor and having some physical form as well as deified form, El is not so definable. El more resembles the unknowable, intangible "God" that we often think of as existing outside of our material world, who does not designate a "chosen people" but is truly the god of the whole world and all people.
Whatever these ancient beliefs really looked like, they were both blended into the books of the Torah (along with two other authors' works, but that's another discussion). However, the theology of "Jews are the chosen people" prevailed for a long time.
[But you can find books in the OT that defy even this principle. The book of Ruth, for example, demonstrates that even foreigners and strangers are to be valued, as the author ends the story by connecting Ruth, a non-Jew who marries into a Jewish household (totally scandalous in the day, worthy of death or at least banishment), to King David, the most powerful and revered king of the Jews. ]
This theology shows up throughout the Bible. When the Assyrians chose to invade Palestine, for example, and succeeded in subjugating the lands, the failure of the Hebrews to withstand this problem was written as the Hebrews losing favor in God's eyes, for turning away from their covenant with God. When the Assyrians were later defeated through Babylonian conquest, that was seen as reward for finally turning back to God and rejecting the religion of the Assyrians (thus, the Babylonians were nothing more than God's way of turning back the Assyrians for the benefit of the Jews). But then, when the Babylonians sacked Jerusalem, burned the Temple and carried off the Jewish royalty, the prophets decreed that the Babylonians were now being used to punish the Hebrews, and they invented the theory that God's punishment is visited doubly upon them for their sins, and through many generations, in order to satisfy God's wrath.
When the Persians destroyed Babylon, that too was viewed as God relenting in his punishment of the Jews. The Greeks conquered Persia, and attempted to subvert Jewish religion. The revolt led by Judas Maccabaeus was seen as successful because the Maccabeans had God on their side, as they were "righteous worshippers."
By Jesus's time, of course, the Jews had been through so much trial and tribulation that the Romans were no more than the latest and worst oppressor yet, and beliefs were strong that the Messiah must come soon to put an end to this supreme evil and finally bring the Jewish Nation into its glory and power.
Whatever Jesus actually did or said, what we are actually left with are four gospels that likely blend a good deal of real sayings and teachings, along with teachings or actions the authors wished to insert to promote belief or particular doctrines. Christianity actually represented a major shift in Judaism, when the apostle Paul took belief in Jesus=Messiah out of the realm of pure Judaism and not only preached to Gentiles (thus bringing the God of Judaism to the entire world) but also did away with the laws of Judaism to help promote Gentile conversion and prevent Gentiles from abandoning the faith. Note that without Paul, and all he said or did to remove the Judaic aspects of belief in Christ, there would be no Christianity today. It would have remained a specific sect of Judaism, and eventually died out.
The significant thing, of course, is that Paul's work, founded on his belief in Jesus's teachings, radically altered the view that Jews were the "chosen people" and brought out the belief in one and only one God, who was the God of the whole world and all people. No matter how you try to reconcile this with the Old Testament, the simple fact remains that the old Yahweh of the OT was NOT the same God that Paul believed in or preached about. Yahweh was a god that belonged to one group of people and belonged very much in physical time and space. Paul's God was far beyond that tribal, nationalistic god.