He agreed to die so that you could have life. It's that simple. His dying opened the way to heaven, defeated Satan, made certain that sin would be removed from Our Universe, and gave you the opportunity to receive eternal life and never die.
Here are some things My servants wrote about that:
(Quoting My Dear Son):
"I am the Resurrection and the Life; he who believes in Me though he was dead, He shall live; and he who lives and believes in Me shall never die."
"He partook of flesh and blood, that through death He might destroy him who had the power of death, that is, the devil [Satan], and deliver them [that's you!] who through fear of death were all their lifetime subject to bondage."
"He carried our sins in His own body on the Cross, so that we, being dead to sins, might live for righteousness."
"[Jesus] God raised up on the third day [after His death], and showed him openly...He is ordained by God to be the Judge of the living and the dead. To Him all the prophets bear witness, that...whoever believes in Him shall receive remission [forgiveness] of their sins."
(Quoting My Dear Son again) "I am the good Shepherd; I give My life for the sheep; My sheep hear My voice, and I know them, and they follow Me; and I give them eternal life, and they shall never perish, nor shall anyone pluck them out of My hand."
Thus We (My Dear Son and I) have connected His death with your life, and we have done so in such a way that they cannot be separated.
So this, My Dear Son's deathday, can become your "new birthday," if you believe that He died and rose again for you, and turn to Him as your "Good Shepherd."