The Keys of Death and Sheol

In the first chapter of the book of Revelation, the risen Yeshua appears and declares that he holds in his hand "the keys to death and Hades." What are these keys and from where did he acquire them? What do they unlock?

This teaching, presented on Erev Rosh HaShanah 5776, discusses the resurrection of the dead in relationship to the shofar of Rosh Hashanah.

Rabbi Yochanah said: The Holy One blessed be He has retained three keys in his own hands and not entrusted them into the hand of any messenger: the Key of Rain, the Key of the Womb, and the Key of the Resurrection of the Dead.” (b.Taanit 2a–b)