What Did Christ Accomplish At Calvary?

Luke 9:28-31
And it came to pass about an eight days after these sayings, he took Peter and John and James, and went up into a mountain to pray.
29 And as he prayed, the fashion of his countenance was altered, and his raiment was white and glistering.
30 And, behold, there talked with him two men, which were Moses and Elias:
31 Who appeared in glory, and spake of his decease which he should accomplish at Jerusalem.