Why is polygamy condemned in the Book of Mormon, but condoned in portions of the D&C (condemned in others) and still believed to be necessary in church doctrine for exaltation in the after-life?

• 为什麽重婚在《摩门经》里面被谴责，却在《教义与圣约》里面部分章节被赦免呢（在其他章节被谴责），并且在教会的教义仍然被相信是死后高升的必要条件呢?