Jesus’ crucifixion was different than the two on either side of him and different than any other crucifixion in human history.  Beyond trembling at the pure agony of the cross, we tremble because of: 

1. Who was on the cross- as the centurion recognized, an innocent man (Lk 23:47), the Son of God (Mt 27:54) - a Divine person, the Creator, who had enough humility to leave the glories of heaven to be made in the likeness of men, to take the form of a bondservant, to be obedient to the point of death, even death on a cross (Phil 2:5-8).  “Well might the sun in darkness hide, and shut its glories in, when Christ the Mighty Maker died for man the creatures’ sin”. 
2. The seriousness of our sins- What an awful punishment that Jesus had to take for our sins, the just for the unjust, to bring us to God (1 Pet 3:18).    “He Himself bore our sins in His body on the cross, so that we might die to sin and live to righteousness; for by His wounds you were healed (1 Pet 2:24; Isa 53:4-6).  All the silver and the gold in the world could not save us from our sins, but only the precious blood of Christ (1 Pet 1:18-19).  The extremely high price of our salvation highlights the seriousness of our crimes. 
3. The love of God for us- How much did God love us?  Enough to give His only begotten Son so that we would not perish because of His righteous anger, but rather live- that is, have a relationship with Him- eternally (Jn 3:16; 1 Jn 4:9-10).  A man might dare to die for a righteous man and even more for a good man, but God sent Christ to die for us while we were ungodly (Rom 5:6-8)- what love!  Thanks be to God for His indescribable gift! (2 Cor 9:15)
4. The hell we have escaped- Because of Jesus’ cross we will be saved from the wrath of God at the Judgment (Rom 5:9).  His wrath will be outpoured on the unforgiven sinner in punishment Jesus described as outer darkness, as a lake of fire, and as pain so severe there will be weeping and gnashing of teeth (Mt 25:30, 41).  And, the worst part about it- this agony will never end! Jesus indicated this with plain figures “where their worm does not die” and “the fire is not quenched” and said to avoid hell at all cost- pluck out your eye, cut off your hand or your foot, that is, whatever extreme measure you have to take to escape it (Mk 9:43-48).  We tremble at Jesus’ cross because, without it, hell would have been our certain destination. 

So think on these things and tremble as you read Douglass Jacoby’s simplified version of Dr. Truman Davis’ description of the agony of crucifixion: 

“Thrown down on His back with arms outstretched along the cross bar, nails were driven through Jesus’ wrists into the wood.  These iron spikes, about 6 inches long and 3/8 inches thick, severed the large sensor median nerve, causing excruciating pain in both arms.  Carefully placed between bones and ligaments, they were able to bear the full weight of the crucified man.  In preparation for the nailing of the feet, Jesus was lifted up and the crossbar fixed to the upright post.  Then with legs bent at the knee, a single nail was used to pierce both feet, one foot being placed over the other.  Again there was severe nerve damage and the pain caused was intense.  It is important to note, however, that neither the wounds to the wrists or feet caused substantial bleeding, since no major arteries were ruptured.  The executioner took care to ensure this, so that death would be slower and the suffering longer.  Now nailed to his cross, the real horror of crucifixion began.  When the wrists were nailed to the crossbar, the elbows were intentionally left in a bent position so that the crucified man would hang with his arms above his head, the weight being taken on the nails in the wrists.  Obviously this was unbearably painful, but it had another effect; it is very difficult to exhale in this position.  In order to breathe out, and then take in fresh air, it was necessary to push the body up on the nailed feet.  When the pain from the feet became unbearable, the victim would again slump down to hang by the arms.  A terrible cycle of pan began:  hanging by the arms, unable to breathe, pushing up on the feet to inhale quickly before again slumping down, and on and on.  This tortured activity became more and more difficult as Jesus’ back was scraped against the upright post, as muscle cramps set in because of the inadequate respiration, and as exhaustion grew more severe.  Jesus suffered in this manner for several hours before, with a final cry, He died.” 

Let Mr. Jacoby’s description help us to picture ourselves at the foot of Jesus’ cross, looking on, and taking in its meaning.  In the words of the old hymn- “Were you there when they nailed Him to the tree, were you there when they nailed Him to the tree, Oh sometimes it causes me to tremble, tremble; were you there when they nailed Him to the tree?”