... Why the difference? Anyone have a good commentary handy?
Gleason Archer in his
Encylopedia of Bible Difficulties (page 135) finds Jamieson-Faucett-Brown's 5-year apprentice explanation reasonably inferred from "careful comparison" of the two passages.
Norman Geisler in his
Big Book of Bible Difficulties (page 98) has a somewhat different explanation. He suggests that there are "distinctions" in the described duties made by each passage: Numbers 4:3 uses the Hebrew word
melakah (Strong's #4399, meaning occupation or business) of the tabernacle; while Numbers 8:24 uses a form of
abodah (Strong's #5656, service or labor) of the tabernacle. He suggests that younger men were limited to the more physical work for at least 5 years before being ordained into administrative services. Unfortunately, I think his particular solution may suffer from the fact that latter verses (4:23, 30, 35, 39, 43, and 47) in Numbers use the word
abodah with the 30-to-50 age group. Although there could be some other distinctions (for example, Numbers 4 seems to be only concerned with the tabernacle on the move, while Numbers 8 seems to be only about when it is erected).
Both Archer and Geisler agree that the lowering of the age to 20 years in Ezra 3:8 was twofold: it was an appropriate adjustment resulting from a short supply of returning Levites out of captivity; and their service was primarly to oversee the restoration of a new temple, not the actual officiating of worship or sacrifices. Geisler acknowledges that David began a tradition of employing Levites from age 20 (Chronicles). Archer reminds us that a boyish Samuel was doing some ministry in the temple (1 Samuel 3:1). These all seem to speak to adjusted levels of authority or responsibility depending upon age.
The Septuagint may give the age 25 at both Numbers passages.