The Old Covenant, the covenant part (the letter of the law) has been abolished, and replaced, but not what we can learn or glean from the OT stories and it's writings...
People want to know why all the great darkness in the OT...? Well, It was time of darkness, and God was filling up the cup-full of the sin(s) of mankind to the full, and making him drink it all up, showing them the fullness (knowledge of) sin and all it's consequences, through experience, Their experience(s), and showing them what seemingly very dark acts might be required to fix it, in some cases...
The Law (letter of the law) makes or made nothing perfect, and far from it and actually makes things much worse, much more sinful, much more dark for mankind...
I don't know if it was a time of saving, maybe only sparing for some IDK...? The Law was given to us to our sin worse, and is that way a curse upon us, if we try to follow and obey the letter of the law, and God brought it upon us and gave it to us in anger back then... So then, the letter of the law is the source of Gods' curse and wrath upon us...
It was not meant to better, improve, or make anything better in any way, at any time, and actually was meant to make things worse...
And very bad, that is why you see so much darkness in the OT...
We are supposed to be free of that now, but I wonder if we really are or will (be)...
If we forget the past we are doomed to repeat it or may have to go through it again, and again, and again...
Who knows...?