Stēkō (G4739) means to stand firm or stand fast — a later form derived from the perfect of histēmi (to stand). It is used exclusively in the NT for the posture of faith under pressure: holding one's ground in the face of opposition, temptation, or trial.
Galatians 5:1 commands: 'Stand firm (stēkete)... do not let yourselves be burdened again by a yoke of slavery.' The entire Reformation doctrine of grace by faith alone was at stake. Philippians 4:1 — 'stand firm in the Lord' — anchors the command in the person of Christ. The believer's standing is not self-generated but received: Christ is the one in whom we stand, and He holds those who are His (Romans 14:4).