My opinion is:-
Just as the Mosaic Law was a "Tutor, leading to the Christ" (Galatians 3:24), the whole of the Old Testament was a Tutor leading to the Christ and the replacement of a vengeful God with a God of Love and mercy.
To appreciate something enough to evoke Love, one has to be aware of its value or necessity.
The Old Testament shows us that God is a frightening being who cannot abide anything but a level of perfection that it is not in mans ability to achieve.
Anything not perfect, including us, he destroys because his world he made has to be perfect, the sin we brought on it was by our own choice.
Having learnt from the Old Testament that we cannot be perfect and earn salvation, even when God tells us how with the Mosaic Law, God then gives us his son to kill to pay the price for our sin.
His son Jesus and the New Testament brings the message that Love is greater than all things, the knowledge that this God of wrath will show mercy causes us to Love him and his son, which in turn qualifies us to benefit from the price Jesus paid, his death instead of ours.
To sum up, we learn from the OT that God is unreasonably demanding, but God in his Love sends Jesus who in effect washes the sin from us before God sees it and kills us because of it. So fear gets replaced by gratitude then Love.
Or, if it wasn't for the OT we wouldn't appreciate how much we need Jesus as the high priest in order to be able to be close to God and gain salvation.
The Quran however, still sees only the frightening aspect of God, not the lengths he has gone to too provide grace where justice is due, the Quran does not appear to have any Love in it, just the sort of fear of a God of torture that far exceeds the Biblical God of death.
Every other page in the Quran seems to be about pain and torture, and speaking to Muslims, they have told me they are so religious because of terror of God, rather than Love for him.