In addition to the noun thrēskia (“expression of devotion to transcendent beings, especially as it expresses itself in cultic rites, worship” BDAG, 459), NT writers and their contemporaries use two other cognate terms, namely the adjective thrēskos (“religious” BDAG, 459) and the verb thrēskeuō (“to practice cultic rites, worship” (BDAG, 459). Only the noun and adjective occur in the NT. We find the noun in Acts 26:5; Colossians 2:18, and James 1:26-27, and the adjective is attested for the first time in Greek literature in James 1:26.
We will consider the use of the noun thrēskia first. When Paul defends himself before Agrippa (Acts 26), Luke includes in Paul’s defense speech that he “conformed to the strictest sect of our religion (tēs hēmeteras thrēskias), living as a Pharisee” (26:5). In the previous verse Paul claims that “all Jews” know this about him and so in the context the noun plainly refers to Jewish religious practices, particularly as the sect of the Pharisees defined and practiced them. Paul associates himself with this religion without apology. Paul employs it one of his letters (Col. 2;18) in the phrase en…thrēskiai tōn aggelōn that the NIV translates as “in the worship of angels.” Since the belief in angels in the ancient world is associated particularly with Judaism, this usage also seems associated with Jewish religious beliefs and practices. Some within Judaism seem to venerate angels in a specific manner. So Jews living in the Diaspora seem comfortable using this term positively to describe the Jewish religion in whole or part.
Two documents associated with Second Temple Judaism also use thrēskia. The Wisdom of Solomon, a document roughly contemporary with Paul or a little earlier, uses this noun twice in reference to idolatry (14:18, 27). In 14.18 he describes the work of the artisan who creates an idol that results eis epitasin…thrēskias (“in intensification of worship/religious veneration”). A few verses later (v. 27) this writer attributes all sorts of sinful behaviours to hē …tōn…eidōlōn thrēskia (“the worship/religious veneration of…idols”). So this noun can refer to non-Jewish worship practices also. In 4 Macc. 5:7 the Syrian King Antiochus describes Eleazar, the Jewish devotee he is threatening to torture, as tēi Ioudaiōn chrōmenos thrēskiai (“one observing the religion of the Jews”). A few verses later (v. 13) he calls it tēsde tēs thrēskias humōn (“this religion of yours”), taunting Eleazar with the idea that the deity whom this religion claims is so powerful surely can forgive some minor transgression.
This noun also occurs in earlier, classical Greek writers such as Herodotus. In his Hist. 2.18.8), 5th century BCE, he describes the vexation of Libyans at the religious principle among Egyptians that forbad the eating of cow’s flesh. A few sections later (Hist. 2.37.14), Herodotus claims that the religious observances practiced by Egyptian priests are myriad. In the middle of the 1st century BCE the Hellenistic historian, Dionysius of Halicarnassus (Ant. Rom. 22.214.171.124), uses this noun to describe some of the cultic rituals practiced by the Romans and traced back to the time of Romulus. Philo, the 1st century CE Hellenistic Jewish scholar uses this noun to describe aspects of the Jewish Religion.
The noun thrēskia refers to the practices humans use to show their devotion to and veneration of deities. Jews and non-Jews employed it for this purpose. Herodotus (Hist. 2.64.3) used the related verb thrēskeuō to describe Egyptian religious observances, such as not entering a temple after intercourse without washing. The author of the Wisdom of Solomon says the wicked thoughts entertained by the Egyptians in their oppression of the Israelites, caused them to err and start worshipping (imperfect tense form (ethrēskeuon 11:15)) irrational serpents (referencing the plagues). The same writer uses this verb in 14.16 to criticize rulers who had statues made for the purposes of worship. Dionysius of Halicarnassus assigns to Romulus the ordering of “the ministers of the gods” (tōn thrēskeuōn tous theous Ant. Rom. 2.23.1), employing the participle of this verb to describe those who were responsible to maintain the appropriate rites for venerating the gods. These usages parallel those discerned previously for the cognate noun.
As noted in the first paragraph, the adjective thrēskos is attested for the first time in Greek literature in James 1:26 and only occurs in this context in the NT. In this part of his letter James discusses the irrationality involved in hearing God’s words, but not acting upon them (1:22-25). Individuals who study God’s words and then perform them experience God’s blessing. He offers a particular example in v. 26. Someone, “who does not strictly control his tongue, but deceiving himself, thinks he is thrēskos, this person’s thrēskia is empty (or worthless).” James has identified the standard by which this person is measuring himself as “the perfect law,” and this seems to locate this individual within a Jewish ideological framework (see 1:25). If this is the case then this “person” in v. 26 would also be Jewish and his religious observances would relate to Yahweh. thrēskos here seems to refer to Jewish religious practices that would entail the worship of Yahweh.
This person, then, regards himself as one who is obedient to the Torah and thus enjoys a covenant relationship with Yahweh. However, the failure of this person to “control his language,” perhaps tantamount to violating the fourth commandment “not to misuse the name of the Lord your God,” worships Yahweh in an empty or worthless manner. In the succeeding verse James equates “pure and undefiled religious practice (thrēskia kathara kai amiantos) before the deity and father (para tōi theōi kai patri)” with care for oppressed people (orphans and widows) and rejection of the world’s values. Religious observance that wins God’s approval expresses both understanding of his word and action that obeys and performs that word.
People incorporated within the newly defined Messianic covenant express a new kind of thrēskia, a kind of religious observance that demonstrates consistency between knowledge of God’s wisdom and will and commitment to practice it with integrity. While it may entail some rituals, this worship gains expression primarily in ethical behaviour that demonstrates intense loyalty to Jesus Messiah and God the father.