God had told them in Exodus, Numbers, and Deuteronomy how to carry the ark, but maybe they forgot, or perhaps they hadn't been meditating on those books recently, so they didn't know how Yahweh wanted the ark transported.
Actually, it would have been difficult to forget how the ark was meant to be carried, because it had two rings on each side for the poles, so that every time they looked at it they would be reminded that Yahweh wanted it to be borne on the shoulders of the priests. We know that they knew the correct way to carry it, because three months after the tragedy with Uzzah, they carried the ark all the way to Jerusalem just as God had told them to transport it (2 Sam. 6:13). The Chronicles version of the incident makes it clear that Yahweh was angry because they weren't carrying the ark properly (1 Chron. 15:11-13).
The timing of Yahweh's anger is also significant here. The text repeatedly informs us that "all" Israel was present (2 Sam. 6:1, 2, 5); a crowd of 30,000 people was watching this parade. With an audience of the entire nation, Yahweh did not want to send the message that obedience was optional, since it was disobedience that earlier led to the loss of the ark and the slaughter by Philistines of 30,000 Israelites (1 Sam. 4:10). Anger displayed in situations of disobedience gets people's attention.
Yahweh's extreme display of anger certainly got the attention of David and the rest of the nation. After the incident with Uzzah, the ark was always carried the right way (2 Sam. 6:13; 15:29; 1 Kings 2:26; 8:3). So it makes sense that Yahweh was mad, because the Israelites should have known better. While Uzzah's death seems harsh, Yahweh had warned them. He told them that if anyone touched the ark, he or she would die (Num. 4:15). Uzzah should not have touched it.
Throughout the Old Testament it was always serious and even dangerous for individuals to come close to the presence of Yahweh (Ex. 3:5; 19:16; 33:20; Judges 6:22-23; 1 Kings 19:11-12; Job 41:10; Ps. 76:7; Mal. 3:2). If Israel's disobedience were the only reason for Yahweh's anger, we might think that he was being petty and harsh, but the next two reasons for Yahweh's anger help explain the severity of the crime.
Riding in the trunk. The second reason Yahweh became mad is that their decision to transport the ark on a cart was not only disobedient, it was also insulting. To understand how a method of transportation could be insulting, we need to recall what the ark represented: the presence of God (Ex. 25:22; Lev. 16:2; 1 Sam. 4:4). Therefore, it warranted extraordinary care. What the law prescribed for the conveyance of the ark was basically a litter (a chair or throne for a distinguished person supported by people carrying poles on each side). Royalty was frequently honored by this method of transport, going back to ancient China and Egypt. King Solomon was carried around on a litter (Song of Sol. 3:7), as was the Syrian ruler Antiochus V (2 Macc. 9:8). It was important for Yahweh's symbolic presence to be treated in a royal fashion because he was their God and King. David needed not to forget that even though he was king over Israel, Yahweh was sovereign over him and the nation.






