Cleric with sword, Jim Holloway's illustration from "This Land is My Land" by Douglas Loss, one of three articles examining the role of the cleric in AD&D with an eye to changes overdue since OD&D, in Dragon 52, August 1981:
According to the D&D game rules, clerics are only allowed to use blunt weapons because they are forbidden to shed blood. This practice was followed during part of the Middle Ages, but not throughout.
Clerics were perhaps limited to blunt weapons because the class was created with medieval Catholicism in mind, and to reduce the cleric's effectiveness in melee; in the Greyhawk supplement, the best one-handed weapon a cleric can use is a mace, which does 1-6 points of damage on man-sized opponents, but fighters can use a sword for 1-8 points. The difference in damage helped separate their fighting ability at low levels -- at higher levels, the cleric is on a less effective combat table than the fighter, and the weapons limitation then seems redundant.
In the Advanced D&D books, the blunt-weapon rule is retained, even though in AD&D a mace is about as good as a longsword, and no form of Christianity is mentioned in the Deities & Demigods Cyclopedia.
The rule should be thrown out. At the very least, a cleric should be able to use the weapon sacred to his god. Is it also not more proper to have clerics use weapons traditional to their culture?