What is the Baptism of Christ's Death?

The fourth baptism we've been learning about in our Family Sunday School hour is the baptism of Christ's death.

It explains what the purpose was of the baptism of Christs' death. And also answers the question of what was in the cup that Jesus drank of.

This lesson is based on Matthew 20:22-23

But Jesus answered and said, Ye know not what ye ask. Are ye able to drink of the cup that I shall drink of, and to be baptized with the baptism that I am baptized with? They say unto him, We are able. And he saith unto them, Ye shall drink indeed of my cup, and be baptized with the baptism that I am baptized with: but to sit on my right hand, and on my left, is not mine to give, but it shall be given to them for whom it is prepared of my Father.