I got this excerpt from Jewish encyclopaedia online
here
—In Post-Biblical Literature:
Josephus, in the main, follows the Biblical narrative, giving the word "Sabbath" the meaning "rest" ("Ant." i. 1, § 1), and controverting the stupid etymology of the name upheld by Apion, according to whom the Jews were forced to observe the Sabbath by the fact of their being afflicted with bubonic boils known in Egyptian by a word similar to the Hebrew word "sabbath" ("Contra Ap." ii., § 2). Moreover, his descriptions of Sabbath celebration do not differ from the Biblical. That the beginning and end of the Sabbath were announced by trumpet-blasts ("B. J." iv. 9, § 12) is shown by the Mishnah (Suk. v. 5).
Josephus makes much of the spread of Sabbath observance in non-Palestinian cities and among non-Jews ("Contra Ap." ii., § 39; comp. Philo, "De Vita Moysis," ii. 137 [ed. Mangey]). That he does not exaggerate is apparent from the comments of Roman writers on the Jewish Sabbath. Horace, in his "Satires" (i. 9, 69), speaks of "tricesima Sabbata," which certainly does not refer to a Sabbath so numbered by the Jews. Juvenal ("Satires," xiv. 96-106), Persius (v. 179-184), Martial (iv. 4, 7), and Seneca (Augustine, "De Civitate Dei," vi. 11) also refer to the Sabbath. In the Maccabean struggle the observance of the Sabbath came to have special significance as distinguishing the faithful from the half-hearted; but Josephus confirms I Macc. ii. 39-41, where the faithful, under Mattathias, decided to resist if attacked on the Sabbath, and not to permit themselves to be destroyed for the sake of literal obedience to the Sabbath law (comp. "Ant." xii. 6, § 2). He mentions instances in which the Jews were taken advantage of on the Sabbath-day—for example, by Ptolemy Lagi ("Ant." xii. 1; xviii. 9, § 2). Still, according to Josephus, the Jews carried on offensive warfare on the Sabbath ("B. J." ii. 19, § 2). Titus was outwitted by the plea that it was unlawful for Jews to treat of peace on the seventh day (ib. iv. 2, § 3). Josephus also publishes decrees exempting Jews from military service on the Sabbath, which exemption gave rise to persecutions under Tiberius ("Ant." xiv. 10, § 12 et seq.). The Essenes are referred to as very rigorous observers of the Sabbath ("B. J." ii. 8, § 9).
In Philo.
In Philo an element of mysticism dominates the interpretation of the Sabbath: the day was really intended for God, a part of whose divine happiness it is to enjoy perfect rest and peace. "Hence the Sabbath, which means 'rest,' is repeatedly said by Moses to be the Sabbath of God, not of men, for the one entity that rests is God." Divine rest, however, does not mean inactivity, but unlabored energy ("De Cherubim," § 26 [i. 154-155]). "Seven" being "the image of God," the seventh day is a pattern of the duty of philosophizing ("De Decalogo," § 20 [ii. 197]). The purpose of man's life being "to follow God" ("De Migratione Abrahami," § 23 [i. 456]), the commandment was given for man to observe the seventh day, ceasing from work, and devoting it to philosophy, contemplation, and the improvement ofcharacter ("De Decalogo," § 20 [ii. 197]). The Sabbath is the most appropriate day for instruction ("De Septenario," § 6 [ii. 282]).
Aristobulus, a predecessor of Philo, wrote a treatise on the Sabbath, fragments of which are extant. Following the Pythagoreans, he enlarges on the marvelous potency of the number "seven," but endeavors, like Philo after him ("De Septenario," §§ 6-7 [ii. 281-284]), to prove the observance of the day to be both reasonable and profitable (Eusebius, "Præparatio Evangelica," xiii. 12, §§ 9-16). He asserts that even Homer and Hesiod observed the Sabbath, citing lines from them and from Linus. According to his understanding, the Sabbath was primarily to be used for searching, the Scriptures, fostering the soul's powers, and striving after the knowledge of truth. The Sabbath might be called the first creation of the (higher) light, in which all is revealed (comp. the benedictions preceding the Shema'; Herzfeld, "Gesch. des Volkes Jisrael," p. 478, Nordhausen, 1867).