Mark 15:33-34 (the 4th Saying from the Cross)

Matthew 27:45-46: "Now from the sixth hour until the ninth hour there was darkness over all the land.  And 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?”

Mark 15:33-34: "Now when the sixth hour had come, there was darkness over the whole land until the ninth hour. And at the ninth hour Jesus cried out with a loud voice, saying, “Eloi, Eloi, lama sabachthani?” which is translated, “My God, My God, why have You forsaken Me?”

THE FOURTH SAYING FROM THE CROSS 
At midday something most dramatic and unusual took place. 
Darkness fell over the land for 3 hours. This represented the terrifying judgement of God.

In this darkness Jesus cried out with a loud voice: 
My God, my God, why have you forsaken me? (Matthew 27:46) 

This is the 4th and Central Saying. It reveals the heart of his mission, the heart of his work on the cross. Christ is God but he is also man. Here he speaks from his humanity- My God (the Father), My God (The Holy-Spirit) He uses 'God' rather than 'Father' because he has lost that intimate fellowship. They'd turned their back on him.

The saying comes from Psalm 22- a detailed prophecy of the sufferings of a crucified man written long before crucifixion was even invented. 
My God, my God, why have you forsaken me? 
Why are you so far from helping me, 
so far from the words of my screaming (roaring) (Psalm 22:1)

In all the physical, emotional and mental torment of his betrayal by Judas, 6 illegal trials, false witnesses, mockings, cursings, spitting, sluggings, beatings, scourgings that Jesus had suffered at the hands of man he was silent (Isa 53:7). All his pain and agony had not caused him to cry out. 
Then when he hung on the cross in extreme pain with his bones pulled apart, where every breath was a torture, with many around him mocking his humiliation - he still did not cry out in pain. No, not once-not until midday when the sun was overhead and suddenly darkness fell. Then in that darkness something happened that made Jesus scream.

What could be so much more terrible that made him scream? In a moment your sins, my sins and the sins of the whole world were put on him and God the Father and God the Holy-Spirit turned their backs on him. He had lived a perfect holy life, hating sin-but now the sin of the world was placed on him. Jesus took our place and bore our sins. He suffered the punishment that we deserved and which justice demanded. He died as a Sin-Offering and paid the penalty for our sin. The wrath and judgement of God that we deserved now fell upon him. (Isa 53:6). In the 3 hours of DARKNESS he suffered the equivalent of eternal hell. He had lived in the fellowship and Presence of God his whole life, even from eternity, but now for the first time he was in darkness, separated from God's presence and blessing (spiritual death) 
Now he drank fully the cup of God's Wrath upon sin. (John 18:11) 

This is the horror that caused him to scream the words: 
My God, my God, why have you forsaken me? (Ps 22:1)

Why did it seem like God turned His back on Jesus? 
Because: Thou are HOLY (v3). Since God is holy He can have nothing to do with sin. At that moment: He who knew no sin was made SIN for us that we might become the righteousness of God in Him (2Cor 5:21). 
So now the full force of God's righteous and holy anger fell on Jesus. 
We cannot imagine the horror he had to suffer. 

What caused him to scream? It was the only thing that could -your sins, my sins, the sins of every person who has ever lived. It was anticipating this in Gethsemene that caused him to sweat blood and ask God to provide another way of bringing our salvation. But there was no other way. He had to drink the bitter cup to the last drop. I'm so glad he did it! If he didn't pay the penalty for our sin, we'd have to pay the price ourselves. 

This is the ultimate revelation of his PERFECT LOVE for us (1John 4:10).

The 4th SALVATION blessing is PROPITIATION - the basis for every blessing. It is only because of Christ's atoning sacrifice that God can freely offer us forgiveness and grace, because he fully satisfied God's Justice. Our greatest need was for someone to take our place, bear the punishment for our sin and set us free from the Wrath of God upon us. The Saying shows that Jesus bore sin and God's wrath for us, so that now God is free to forgive and bring us back to Himself and pour out His grace, mercy and blessings upon us. Jesus spoke these words, showing that he was bearing our spiritual death and separation from God on the cross, in order that we can be re-united to God and receive His eternal and abundant life. 

These words were spoken from the cross to God to reveal that flowing out from the cross GODWARD, was a propitiation, satisfying God's Justice and appeasing His anger upon sin. 

This in turn freed Him to pour out His abundant mercy and life upon mankind. Thus this central saying reveals the central aspect of the work of the cross- which by satisfying God's Righteousness, provides the basis for every blessing of God.

Jesus bore the sin of the whole world so that forgiveness and salvation is available to all through Christ. 

Now it's up to each individual to accept or reject God's offer of Mercy.

To the believer the propitiatory sacrifice of Christ is the basis for receiving all of God's grace, and results in a life of gratitude to God, lived to please and glorify Him.

To the unbeliever it is a warning - that if God did not spare his Son when your sin was upon him, then He will not spare you in the judgement if your sin is still upon you, as it surely will be, if you have rejected the forgiveness and salvation from sin provided through Christ's atoning sacrifice.