Then Judas assembled his army and went to the city of Adullam: Adullam was a town between Jerusalem and Marisa, about 25 kilometers (15 miles) southwest of Jerusalem.

As the seventh day was coming on: The seventh day is the Sabbath. This clause may be translated “Since it was only a few hours before the Sabbath began [or, the beginning of Sabbath].”

They purified themselves according to the custom: They purified themselves refers to a ritual washing, probably a bath involving the whole body. It was done according to the custom, not the law, since there is nothing in Jewish law requiring a ritual purification before the Sabbath. However, Judas’ men were especially religious men, and could easily have gone farther than the Law required. Therefore it probably would be more accurate to say “their custom” rather than “Jewish custom” (Good News Bible).

And they kept the sabbath there: The adverb there refers to Adullam.

Here is an alternative model for this verse:

• After the battle Judas led his troops to the town of Adullam. Since it was only a few hours until the Sabbath, they bathed to make themselves ritually pure for the Sabbath, as was their custom [or, as they always did]. They observed [or, celebrated] the Sabbath in Adullam.

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Maccabees. (UBS Helps for Translators). New York: UBS, 2011. For this and other handbooks for translators see here.