The verb proskartereō occurs in the New Testament primarily in Mark’s Gospel (3:9), Acts (1:14; 2:42,46; 6:4; 8:13; 10:7), and Paul’s letters (Romans 12:12; 13:6; Colossians 4:2). Paul also used the cognate noun proskarterēsis at Ephesians 6:18. In The simple form kartareō (“to be steadfast, patient”) occurs once in Hebrews 11:27, with the sense of “continue, persevere.” The cognate adjective karteros (“steadfast, patient, strong”). Paul’s usage this verb twice is associated with prayer (Romans 12:12; Colossians 4:2), as it also is in Acts 1:14; 6:4. The compound form of the verb probably expresses a strengthened form of this sense of “persistent continuation, strong adherence to something/someone, be busy with.” The verbal root is related to the Greek lexeme kratos “power, authority.”
The compound verb occurs frequently in classical and Hellenistic Greek writers and inscriptions. It can describe loyalty to a person. For example, the Demosthenes in Neaeram (Sp.) 120.6 claims: παραδοῦναι τὰς θεραπαίνας τὰς Νεαίρᾳ τότε προσκαρτερούσας ὅτ’ ἦλθεν ὡς Στέφανον ἐκ Μεγάρων, Θρᾷτταν καὶ Κοκκαλίνην, “(I proposed that) then when she comes as Stephen from Megara, he should deliver up for the torture the women-servants, Thratta and Coccalinê, who remained loyal with Neaera.” The verb also can convey the idea of “pay persistent attention to” as we find in Polybius Historiae 1.55.4 ἀλλ’ οἱ μὲν ἐχορήγουν κατὰ γῆν ἀπροφασίστως, οἱ δὲ προσεκαρτέρουν ταύτῃ κατὰ τὸ δυνατόν “but some were sending provisions overland constantly; and others were persisting in the siege as strongly as they could.” Similarly we find in Polybius Historiae 1.59.12 the sense “to hold fast to something” (τῇ τε λοιπῇ τῇ κατὰ τὴν δίαιταν ἐπιμελείᾳ προσκαρτερῶν “and by holding fast to diligence in a disciplined way….”). In the account of the spies (Numbers 13) the Greek translation uses this verb in the sense of “persevere” (προσκαρτερήσαντες λήμψεσθε ἀπὸ τῶν καρπῶν τῆς γῆς “and you shall persevere and take some of the fruit of the land” (NETS translation)).
The earliest usage in the New Testament occurs in Paul’s letters. He employs it first in Romans to express two distinct but related ideas. In 13:6 Paul describes secular public servants as essential agents in God’s purposes as “they devote (proskarterountes) themselves to this very purpose (i.e., collecting taxes (13:6); promoting good and restraining evil (13:3-4; or perhaps their specific service).” Earlier in Romans 12:12 he describes believers as “devoted to/steadfast (proskarterountes) in prayer.” In this same verse we encouragements to “endure in affliction” and “participate in/share in the needs of the holy ones.” Paul urges the believers in the Colosse church to “be devoted to prayer…praying together also for us” (Colossians 4:2). This is one way they remain “spiritually vigilant with thanksgiving” and partner together with him in the gospel mission. Paul uses the cognate noun at Ephesians 6:18 in the same sense, linking it by means of an adverbial phrase of instrument with the participle agrupnountes, “lying sleepless, keeping awake and thus vigilant in complete devotion (en pasēi proskarterēsei)/adherence and petition concerning all the holy ones.”
Perhaps the writer of Luke-Acts followed Paul’s lead in the use of this verb to describe Christian spiritual activities. The earliest Christians, according to Acts 1:14, were “devoting themselves to/adhering to/persisting in (proskarterountes) prayer.” This the same idiom Paul used in Romans 12:12 and Colossians 4:2. In the same vein we read that the early Jewish Christians “were devoting themselves to/adhering to/persisting in (ēsan…proskarterountes) the apostles’ teaching” (Acts 2:42). Everyone “continued (proskarterountes) together each day in the temple” (Acts 2:46).The apostles define their role in the Jerusalem church as “devoted /steadfast (proskarterēsomen) in prayer and the service of the message” (Acts 6:4), in distinction from service for the widows.
The author of Luke-Acts also used this verb to describe the personal attentiveness of assistants to their supervisors. For example, in 10:7 we learn that Cornelius, a Roman centurion staying in Caesarea, had “two servants and a devout solder who (plural reference) attended personally (tōn proskarterountōn) to his needs.” The verb describes how a person adheres to, continues with, remains steadfast to” another person. Simon, the convert in Samaria, after he was baptized, “was staying close (ēn proskarterōn) to Philip” (Acts 8:13). The verb also occurs once in Mark’s Gospel (3:9) where Jesus commands his followers to have a small boat kept close by (proskarterēi) for his use lest the crowds throng him, a meaning that is similar to the occurrence in Acts 8:13.
According to Grundmann (Theological Dictionary of the New Testament, III, 617) kartareō “is a term used in Gk. ethics with reference to the right attitude and conduct of the wise.” It occurs frequently in 4 Maccabees (roughly contemporaneous with Paul’s writings) with the sense of “endure” in the face of unjust religious oppression. Such endurance demonstrated by Moses in the context of Hebrews 11:27 arises from his faith in Yahweh and his purposes. When early Christian leaders urge believers to “persist in/be devoted to prayer,” they propose a habit of prayer somewhat different from the Jewish pattern of daily prayers at specific hours of the day. It also suggests that the way believers dealt with rising and consistent hostility was through a persistent reliance upon God and the Holy Spirit.