Elder Russell M. Nelson of the Quorum of the Twelve Apostles explained several ways in which the Atonement is infinite:
“His Atonement is infinite—without an end. It was also infinite in that all humankind would be saved from never-ending death. It was infinite in terms of His immense suffering. It was infinite in time, putting an end to the preceding prototype of animal sacrifice. It was infinite in scope—it was to be done once for all. And the mercy of the Atonement extends not only to an infinite number of people, but also to an infinite number of worlds created by Him. It was infinite beyond any human scale of measurement or mortal comprehension.
“Jesus was the only one who could offer such an infinite atonement, since He was born of a mortal mother and an immortal Father. Because of that unique birthright, Jesus was an infinite Being” (in Conference Report, Oct. 1996, 46; or Ensign, Nov. 1996, 35).