Good News Translation‘s paragraph break here is appropriate since there is a slight shift in the subject matter.

Moses ordained him, and anointed him with holy oil: Ordained him is literally “filled his hands,” which is a Hebrew idiom. The ordination of Aaron is described in Lev 8. A person became a priest by being ordained to office. Part of the ceremony was anointing—pouring olive oil over the head of the man becoming a priest. Holy oil is olive oil only used for sacred occasions. It was thus taboo, and in some languages “taboo oil” will be the more natural translation.

It was an everlasting covenant for him and for his descendants all the days of heaven: All the days of heaven means “forever.” It would be in order to render these lines as follows: “The Lord made an eternal covenant [or, agreement] with Aaron and his descendants forever.”

To minister to the Lord and serve as priest and bless his people in his name: The Lord is literally “him,” but Revised Standard Version spells out the pronoun for clarity. To minister to the Lord is translated better in New Jerusalem Bible, which says “that he should preside over worship.” However, Good News Translation is good also. For these lines we could say “that they should act as priests, leading in worship and blessing the people in the Lord’s name.”

An alternative model for this verse is:

• Moses ordained Aaron as priest by pouring sacred [or, taboo] olive oil on his head. And the Lord made an eternal covenant [or, agreement] with Aaron and his descendants that they would act as priests forever, leading the people in worship and blessing them in the Lord’s name.

In some languages, however, it will be necessary to break up the second sentence into shorter sentences; for example:

• … At the same time the Lord made an agreement with Aaron and his descendants. This agreement said that Aaron and his descendants would serve as priests forever. In this position they would lead the people in worship and bless them in the Lord’s name [or, call upon the Lord to be kind and good to them].

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on Sirach. (UBS Helps for Translators). New York: UBS, 2008. For this and other handbooks for translators see here.