He and his father-in-law were resolved not to be outdone by the Jews.

They in Samaria would build a grand temple, just as the Jews had done in Jerusalem.

One hill was as good as another, so they thought; their own Gerizim, with its lovely trees and its sunny slopes, was as fair or fairer than Mount Moriah.
So they set to work with all their energy, to build the rival temple on the very hill where 1000 years before, in the time of Joshua, the blessings of the law had been read, whilst the curses were pronounced from the hill on the opposite side of the valley, Mount Ebal.
Here then, on Gerizim, the mount of blessing, rose the new temple, which was built with one object in view, that it might outvie in splendour the one in Jerusalem.

When it was finished, Manasseh was made the rival high priest, and was able to do what he liked, and to exercise his authority in any way he pleased in his father-in-law's province.
Nor was Manasseh the only priest in the Gerizim temple; many other runaway priests joined him, all who were angry with Nehemiah, all who were offended or touchy, all who thought themselves injured in any way, all who had been found fault with for Sabbath-breaking or for any other sin, left Jerusalem for Samaria--chose the temple of Mount Gerizim instead of the holy temple on Mount Moriah.
Yet of the Samaritans it is said: 'They feared the Lord, and served their own gods.' It was a half-and-half religion, Judaism and heathenism mixed up together, the worship of God and the worship of idols side by side.
Satan, now-a-days, has his modern temple of Gerizim.

He does not try to lead nominal Christians to throw up religion altogether, for he sees that it would be of no use to do so.