The original Jehovah is one of those antropomorphic gods that are typical for Europe and the Middle-East. (I think, Jehovah is the only remaining god, the war-god, of an older jewish polytheistic religion. And that this polytheistic religion was turned into a monotheistic religion during the babylonian exile as a penance: They didn't worship Jehovah enough because they worshipped other gods beside him and that's why they lost the war with the Babylonians. That's why they no longer worshipped deities like Ashera and focused exclusively on Jehovah from this point onwards.)
The Jehovah of the New Testament is a totally different kind of god. From a tyrant-figure, a war-god, he gets turned into the supreme being of a complex cosmology. The Jews don't have a hell. And a close reading of the Old Testament reveals that Satan is more of a "trickster"-entity than an evil/antagonistic entity. The antagonism God-vs-Lucifer exists only in the New Testament.
The New Testament is also the source where God gets elevated to being the best of all things. He is the biggest everything. And this increase in profile can only be substantiated if you have successes to show off. The New Testament does this by defining Lucifer as the perfect example of everything that is wrong: Lucifer's sin is to not worship God despite worshipping God being the "correct" thing to do. Because he's best.
Lucifer tempting Jesus in the desert is an excellent example: Jesus is in no way beating Lucifer's challenges to his godliness. He wiggles his way out of the challenges and uses them as a pretext to say that it's wrong to even doubt and test God. Compare that to the Old Testament where God is meddling all the time with the lives of people.
The Old and the New Testament should really be read separately.
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