"And We had certainly given Moses the Scripture, but it was disagreed upon," meaning: a group believed in it, and a group disbelieved in it. "And if not for a word that preceded from your Lord," which is that He would not hasten the punishment of the Hereafter within the worldly life,

"the matter would have been decided between them," meaning: Allah would have judged between them in this world, admitting the people of Paradise into Paradise and the people of the Fire into the Fire, but He has delayed that until the Day of Resurrection.