Why was the man who touched the ark to keep it from falling killed by God? Wouldn't it just be a instinctive response to grasp something that was about to fall? It seems to cruel that God would do this.
The event that you are referring to is found in 2 Samuel 6:3-8 and in 1 Chronicles 13:6-12.
And David and all Israel went up to Baalah, that is, to Kiriath-jearim, which belongs to Judah, to bring up from there the ark of God, the LORD who is enthroned above the cherubim, where His name is called. And they carried the ark of God on a new cart from the house of Abinadab, and Uzza and Ahio drove the cart. And David and all Israel were celebrating before God with all their might, even with songs and with lyres, harps, tambourines, cymbals, and with trumpets. When they came to the threshing floor of Chidon, Uzza put out his hand to hold the ark, because the oxen nearly upset it. And the anger of the LORD burned against Uzza, so He struck him down because he put out his hand to the ark; and he died there before God. Then David became angry because of the LORD’S outburst against Uzza; and he called that place Perez-uzza to this day. And David was afraid of God that day, saying, “How can I bring the ark of God home to me?” (NASB) 1 Chronicles 13:6-12
In 2 Samuel 6 we find some more details since it records the same event. Here is a portion of the passage.
But when they came to the threshing floor of Nacon, Uzzah reached out toward the ark of God and took hold of it, for the oxen nearly upset it. And the anger of the LORD burned against Uzzah, and God struck him down there for his irreverence; and he died there by the ark of God. (NASB) 2 Samuel 6:6-7
Here we discover that Uzza’s name can also be spelled as Uzzah and that the threshing floor of Chidon was also referred to as Nacon (2 Sam. 6:6). Why did this happen?
Do Not See or Touch! The ark of God was one of the holy objects . God had made it clear to the Israelites during the time of Moses that they were not to touch the holy objects associated with the tabernacle worship (Numbers 4:4-6, 15-20).
And when Aaron and his sons have finished covering the holy objects and all the furnishings of the sanctuary, when the camp is to set out, after that the sons of Kohath shall come to carry them, so that they may not touch the holy objects and die. These are the things in the tent of meeting which the sons of Kohath are to carry . . . But do this to them that they may live and not die when they approach the most holy objects: Aaron and his sons shall go in and assign each of them to his work and to his load; but they shall not go in to see the holy objects even for a moment, lest they die.” (NASB) Numbers 4:15, 19-20
On occasions the Israelites needed to move the tabernacle. Therefore, God had given the Israelites directions as to how to move it. The descendants of Kohath, called Kohathites, were the only priests who were allowed to move the tabernacle. But they were not allowed to see or touch the holy objects. If anyone touched a holy object or saw one he or she would die. Therefore, the priests were to cover the holy objects so that the Kohatites would not die during the move (Num. 4:19-20).
Just Helping? From Numbers 4:4-20, 2 Samuel 6:3-8, and 1 Chronicles 13:6-12 we discover that two Kohathites, Uzzah and Ahio, drove the cart during the move. The cart was pulled by oxen. The ark of God had been put on a cart. This was a violation of God’s command in Numbers 7:9 which directed the Kohathites to carry the holy objects on their shoulders. Why didn’t God strike them dead when they placed the holy objects on the cart and started the move? I believe that God showed them His mercy and forgiveness at the start of the trip.
The oxen driven cart eventually came to the threshing floor of Nacon, and apparently Uzzah and Ahio had trouble with the oxen. We are not told exactly what happened. The oxen must have been causing the cart to sway and tilt and when the cart came to the threshing floor, the ark of God almost fell over. This would not have happened if the holy objects had been carried on the Kohathites’ shoulders. 2 Samuel 6:6 says that Uzzah did not just reach out to stop the ark from falling. He responded by “taking hold of it.” The Hebrew word means that he grasped and apparently briefly held on to it. Why hold on to it? Would God have taken his life if he had just quickly put out his hand and pulled it back? Did he hold on to some uncovered part of it? We do not know. but it is clear that this was a second violation.
God had directed them to carry the holy things on their shoulders. They did not. Putting them on a cart was a planned violation. No one died. The second violation, while not planned, was also an intentional violation, and God finally responded. They missed the fact that God called these items holy. Both King David and the priests ignored the fact that God had spoken. Were Uzzah and Ahio glad that God did not kill them when they loaded the holy objects on the cart? Did they think that God was not serious? When we ignore God’s desires, we are ignoring Him. He wants our love and submission.