One must always keep in mind that the bible is a progressive revelation of God and God's will, cumulating in The Word of God incarnate among us, Jesus Christ.
God doesn't change, but our understanding of him does, hence the supposed contridiction at times or differences between God in the OT and God as revealed correctly in His Son Jesus Christ.
I am not saying that the NT superceeds the OT, just that the NT "clears" up many of the erronesous man-made views in the OT.
And one of those views was that God was full of wraith and hate and vengenace.
IN the OT the prophets spoke in a way that they could speak in realtion to WHO they were speaking too, withen the context of the genre they were writing, some of it was historical, some was rhetoric and some was revelatory.
But these issues were present even in the earliest stages of the Chucrh, to say that it is nouvec-christians interpreting things their way is showing lack of understanding about the history of the church.