Clement of Rome, 1 Clement 40
Since these truths are obvious to us and we have been plunged into the depths of divine knowledge, we must do everything in an orderly way — everything the Master commanded to be done at appointed times. He commanded that offerings and services be carried out, not haphazardly or in disorder, but at set times and hours. He himself determined by his supreme will where and through whom they should be done, so that everything done may be holy and acceptable to his good pleasure. Therefore those who present their offerings at the appointed times are acceptable and blessed, because by following the Master's lawful commands they do not sin. Distinct services have been assigned to the high priest, a specific place has been appointed for the priests, particular ministries are laid on the Levites, and the lay person is bound by the precepts for the laity.
Greek
Προδήλων οὖν ἡμῖν ὄντων τούτων, καὶ ἐγκεκυφότες εἰς τὰ βάθη τῆς θείας γνώσεως. πάντα τάξει ποιεῖν ὀφείλομεν, ὅσα ὁ δεσπότης ἐπιτελεῖν ἐκέλευσεν κατὰ καιροὺς τεταγμένους. τάς τε προσφορὰς καὶ λειτουργίας ἐπιτελεῖσθαι, καὶ οὐκ εἰκῆ ἢ ἀτάκτως ἐκέλευσεν γίνεσθαι, ἀλλ’ ὡρισμένοις καιροῖς καὶ ὥραις. ποῦ τε καὶ διὰ τίνων ἐπιτελεῖσθαι θέλει, αὐτὸς ὥρισεν τῇ ὑπερτάτῳ αὐτοῦ βουλήσει. ἵν’ ὁσίως πάντα γινόμενα ἐν εὐδοκήσει εὐπρόσδεκτα εἴη τῷ θελήματι αὐτοῦ. οἱ οὖν τοῖς προστεταγμένοις καιροῖς ποιοῦντες τὰς προσφορὰς αὐτῶν εὐπρόσδεκτοί τε καὶ μακάριοι: τοῖς γὰρ νομίμοις τοῦ δεσπότου ἀκολουθοῦντες οὐ διαμαρτάνουσιν. τῷ γὰρ ἀρχιερεῖ ἴδιαι λειτουργίαι δεδομέναι εἰσίν, καὶ τοῖς ἱερεῦσιν ἴδιος ὁ τόπος προστέτακται, καὶ Λευΐταις ἴδιαι διακονίαι ἐπίκεινται: ὁ λαϊκὸς ἄνθρωπος τοῖς λαῖκοῖς προστάγμασιν δέδεται.