We can analyse paganism, monotheism and Christianity from the perspective of the implied relationship between Man and the divine (and an understanding of the nature of divine).
Paganism is hugely varied, each tribe and locality having
its own version, and most are fluid and loosely defined - with no real
attempt to hold it constant. The gods (the many little 'g'-gods) are more powerful than, but not
qualitatively different from, Men. The gods are subject to the same virtues and
sins as Men; have the same kind of strengths and weaknesses - therefore the
religion is one of divination and propitiation - of Men discerning the will of the gods, and attempting to influence the gods by flattery, sacrifice etc
Monotheistic religions (such as Judaism and Islam) have a creator deity - a capital-G God; and the practice is underpinned by obedience to that God (obedience to laws/ rules/ rituals as revealed by prophets who are merely mouthpieces of the divine). The relationship between Man and God is one of the infinitely-lesser submitting to the incomprehensibly-greater - and how people feel about this is pretty irrelevant. The religion is therefore one of practice, not belief; and the ethic one of strict adherence to the rules of practice.
(There is no divination or sacrifice in monotheism, as such - since God is so infinitely removed and great; that it would be impossible to understand, predict or influence such a God.)
What of Christianity? Well, although self-identified Christianity is often corrupted by Monotheistic or Pagan elements - the intrinsic nature of Christianity is different from either.
Christianity focuses on Jesus - and on the one hand Jesus was not 'a god' (as he might be in paganism - e.g. a god in human form) - because, for Christians, Jesus lived in a reality where there was a unified creator deity - a prime God who was not Jesus.
But Jesus was divine, and brought the teaching that all Men could (by following him) also become divine (via death and resurrection).
In what sense was Jesus, the Man, also divine? Because by some means - such as the divine spirit impregnating Jesus's Mother, or the divine spirit descending upon Jesus at baptism - Jesus the Man was made god. But not just made-into 'a' god; but made a god-creator who could, and does, work-with God the prime creator.
Therefore Jesus became 'fully divine'; that is, he eventually joined-with the divine creator in the work of creation, while remaining a Man; and Jesus made it possible for other Men to do the same.
So, Christianity takes the understanding of God as the single, original prime creator from monotheism; and takes the continuity between gods and Man (the possibility of a man becoming a god) from paganism, and made a new category of god-creator - the two being brought-together in and by the centrality of Jesus Christ.
(Of course, I am assuming here that Christianity is Obviously Not a type of monotheism; which many theologians have always asserted it is - fudging the issue by Trinitarian incoherence. Evidence for the wrongness of the idea of Christian monotheism is that when Christianity has been so regarded, it takes on the qualities of monotheism - becomes essentially like Judaism and/ or Islam; that is a religion of obedience, law, ritual, submission - as contrasted with being distinctively 'Christian', as Jesus was and taught.)