Commentary for I Chronicles 22:8

And when he said, "You have shed blood abundantly" – for there was innocent blood among the blood that he shed, like the blood of Uriya, and this happened before. Also regarding the blood of the priests, he was the reason, as he said, "I have occasioned the death of all the persons of your father's house" (I Shmuel 22:22). Also among the blood of the nations that he shed, it is possible that there were good and pious people among them. Nevertheless, he was not punished for them because his intention was to destroy the wicked that they not attack Israel and to save himself when he was in the land of the Philistines, and therefore he spared no man or woman. But since he was involved in abundant bloodshed, God barred him from building a Temple, which is for peace and atonement of sin and the crown of prayer, as He forbade the waving of iron over the altar and in the Temple. Since iron is used for the production of tools of death, it should not be used for the production of tools of peace.