Several times in the New Testament the writers describe how God acts to “make firm or strengthen” the Messiah’s followers (Romans 16:25; 1 Thessalonians 3;13; 2 Thessalonians 2:17; 3:3; 1 Peter 5:10). In other contexts the writers or human characters in the narrative purpose to strengthen others in the faith (Luke 22:32; Acts 18:23; Romans 1:11; 1 Thessalonians 3:22; 2 Peter 1:12). Twice believers are urged to “strengthen their hearts” (James 5:8) or their faith (community?) (Revelation 3:2). The writer of Luke’s Gospel says that Jesus “made his face strong to journey to Jerusalem” (Luke 9:51), describing the Messiah’s determination and commitment to complete his divine mission. The forms of this verb in the New Testament are active in voice, except for Luke 16:26 that speaks of “the great chasm fixed” and Romans 1:11 where Paul desires to enable the Roman Christians “to stand fast,” similar to Peter’s concern in 2 Peter 1:12. In addition all uses seem to be transitive, having an explicit or implied object. In the New Testament It always seems to have a positive implication. In contrast the Exodus narrative uses the idea of “making the heart strong” to describe Pharaoh’s resistance to Yahweh in the Plague stories, a Hebrew idiom that the translator renders with a different Greek verb.
The verb form stērizō is causative, i.e., it expresses the idea that the subject is causing or making someone or something firm in its place, fixed, propped up, and so the object becomes established or is metaphorically confirmed and made inwardly firm. In the case of Jesus (Luke 9:51), he set or made firm his face to journey to Jerusalem. This expression reflects a Hebrew verb phrase found in texts such as Genesis 31:21; Ezekiel 21:2; Jeremiah 44:12, in which an agent determines to reach a destination or to bring it harm.
Another idiom that has its roots in the Hebrew scriptures occurs in James 5:8 — fix one’s heart upon and therefore to pay attention to something. In the Old Testament Plague Narrative, Egyptians who “did not fix their heart,” i.e., show any concern about or pay any attention to Yahweh’s warning, discovered their herds destroyed by the plague of hail (Exodus 9:21). This Hebrew verbal phrase can also mean “refresh oneself” with food (i.e., to fortify oneself) or drink of some other provision in preparation from some arduous activity (e.g., Judges 19:5, 8; Psalm 103:15) or “to take courage” (e.g., Psalm 111:7; 1 Thessalonians 3:22). These verbal phrases, i.e., “fix the face, fix the heart,” are not found in Greek writings outside the Biblical texts, or apocryphal writings such as Sirach, until the Christian era. So it seems the use of the verb in Luke 9:51 and other New Testament context owes something to the usage of Hebrew idiom and its translation in the Septuagint.
Returning to 2 Thessalonians 2:17, Paul expresses his prayer for these new Christians that God will give them the moral and spiritual courage to remain committed to the gospel, despite the hardships they may experience. Although the object “your hearts” (humōn tas kardias) is only explicit with the previous infinitive, it is implied with stērixai. The infinitive clauses are joined with the conjunction kai (and). The infinitive form functions as an imperative in this context. The adverbial prepositional phrase (en panti ergōi kai logōi agathōi) references what should be affected in some way by this divine action, namely their persistent commitment to “every good task and message.” It has an ethical outcome that demonstrates the change produced by the gospel and their new relationship with God through Jesus Christ. Paul describes some of the blessings of their new faith in v. 16 and these new realities should provide comfort and determination to persist in this faith (e.g., Psalm 112.8). In 3:3 Paul states that God links his intention to help them persevere with his commitment to protect them from the evil one. According to 1 Peter 5:10 God’s actions ultimately have an eschatological purpose.
Although God involves himself in these spiritual activities, he also uses other believers to develop this spirit of endurance and strength, as well as desire to keep doing what is good. Sometimes the example of other believers serves this purpose and sometimes it is their message. God is intentional in his desire and initiatives to enable his people to remain loyal to himself and the gospel. It is those who fear God whom God strengthens.