Ergazomai is the verb for working or laboring — performing tasks with sustained effort. It can describe physical labor (Matt 21:28 — working in a vineyard), trade and commerce (Matt 25:16 — putting money to work), and spiritual activity (Jn 6:28 — doing the works God requires; Jn 9:4 — working while it is day). It is the root of ergon (work/deed) and ergatēs (worker). In Paul's theology it stands in contrast to pisteuō (believe) and charis (grace) — justification is not by ergazomai (Rom 4:4-5).
Paul's crucial use of ergazomai in Romans 4:4-5 shapes the entire Protestant doctrine of justification: 'Now to the one who ergazomai, wages are not credited as a gift but as an obligation. However, to the one who does not work [ergazomai] but trusts God who justifies the ungodly, their faith is credited as righteousness.' Salvation is not earned labor but received gift. Yet Jesus' use in John 9:4 — 'We must work [ergazomai] the works of him who sent me while it is day' — shows that those who are saved are energized to labor for the kingdom. Grace precedes works; but where grace truly arrives, it always produces works.