"I am the good shepherd, and I know My own and My own know Me, even as the Father knows Me and I know the Father; and I lay down My life for the sheep. I have other sheep, which are not of this fold; I must bring them also, and they will hear My voice; and they will become one flock with one shepherd. For this reason the Father loves Me, because I lay down My life so that I may take it again. No one has taken it away from Me, but I lay it down on My own initiative. I have authority to lay it down, and I have authority to take it up again. This commandment I received from My Father."
Furthermore, his death has a purpose, and indeed had a purpose hundreds of years before it happened:
Who has believed our message? And to whom has the arm of the LORD been revealed? For He grew up before Him like a tender shoot, And like a root out of parched ground; He has no stately form or majesty That we should look upon Him, Nor appearance that we should be attracted to Him. He was despised and forsaken of men, A man of sorrows and acquainted with grief; And like one from whom men hide their face He was despised, and we did not esteem Him. Surely our griefs He Himself bore, And our sorrows He carried; Yet we ourselves esteemed Him stricken, Smitten of God, and afflicted. But He was pierced through for our transgressions, He was crushed for our iniquities; The chastening for our well-being fell upon Him, And by His scourging we are healed. All of us like sheep have gone astray, Each of us has turned to his own way; But the LORD has caused the iniquity of us all To fall on Him. He was oppressed and He was afflicted, Yet He did not open His mouth; Like a lamb that is led to slaughter, And like a sheep that is silent before its shearers, So He did not open His mouth. By oppression and judgment He was taken away; And as for His generation, who considered That He was cut off out of the land of the living For the transgression of my people, to whom the stroke was due? His grave was assigned with wicked men, Yet He was with a rich man in His death, Because He had done no violence, Nor was there any deceit in His mouth.
His death was not a meaningless tragedy, but a purposeful sacrifice on our behalf. There was more to his sacrifice than the physical sacrifice, however. He suffered our punishment, not just death, but abandonment by God.
About the ninth hour Jesus cried out with a loud voice, saying, "Eli, eli, lama sabachthani?" that is, "My God, my God, why have you forsaken me?"
Christians believe that these words are not merely a cry of desperation, quoting Psalm 22:1, but that it is the literal truth that Jesus was abandoned by God, who turned his face from his own Son when he became sin for our sake. In so doing he not only made forgiveness possible, he made it possible for us to be a part of the relationship he and the Father once shared and would share again:
But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name. Which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God.
So, while this is a day to mourn what Jesus suffered, to mourn that our condition made it necessary for him to suffer in this way, Good Friday is good because the greatest good came out of Jesus's death. This is what redemption is all about, when God makes what is bad, even evil, good, by buying it back and making it his own again. I'll conclude with Matthew's account of Jesus's death, part of which I've already quoted:
Now from the sixth hour darkness fell upon all the land until the ninth hour. About the ninth hour Jesus cried out with a loud voice, saying, "Eli, eli, lama sabachthani?" that is, "My God, my God, why have you forsaken me?" And some of those who were standing there, when they heard it, began saying, "This man is calling for Elijah." Immediately one of them ran, and taking a sponge, he filled it with sour wine and put it on a reed, and gave Him a drink. But the rest of them said, "Let us see whether Elijah will come to save Him." And Jesus cried out again with a loud voice, and yielded up His spirit. And behold, the veil of the temple was torn in two from top to bottom; and the earth shook and the rocks were split. The tombs were opened, and many bodies of the saints who had fallen asleep were raised; and coming out of the tombs after His resurrection they entered the holy city and appeared to many. Now the centurion, and those who were with him keeping guard over Jesus, when they saw the earthquake and the things that were happening, became very frightened and said, "Truly this was the Son of God!"
It is an occasion for solemnity, but also an occasion to remember that God brings good out of evil.