seeing that aforetime they had been bent on denying the truth, and had been wont to cast scorn, from far away, on something that was beyond the reach of human perception?

Seeing that they did reject Faith (entirely) before, and that they (continually) cast (slanders) on the unseen from a position far off?

When they disbelieved in it of yore. They aim at the unseen from afar off.

And they indeed disbelieved in it before, and they utter conjectures with regard to the unseen from a distant place.

And they had already disbelieved in it before and would assault the unseen from a place far away.