The Greek adverb, aksiws, is translated "worthy of" in all six of its New Testament uses in the NASB. Five of those uses refer to our acting "worthy of God" or the gospel or our heavenly calling. What does this mean? Does it mean that we are to become "worth" God's favor? That is, does "worthy of" mean - deserving or meriting or earning God's favor? Does it call attention to our worth which God is obliged to acknowledge because it enriches his worth, the way a great computer programmer might be worth $200,000 to Microsoft?
Here are all five of these uses:
3 John 1:6, "You will do well to send them on their way in a manner worthy of God."
Thessalonians 2:12, "Walk in a manner worthy of the God who calls you into His own kingdom and glory."
Colossians 1:10, "Walk in a manner worthy of the Lord, to please Him in all respects, bearing fruit in every good work and increasing in the knowledge of God."
Philippians 1:27, "Conduct yourselves in a manner worthy of the gospel of Christ."
Ephesians 4:1, "Walk in a manner worthy of the calling with which you have been called."
I don't think these texts mean that we merit from God or the gospel or our call; but that they merit from us. That is, to "walk worthy of the Lord" means to walk in a way that the Lord deserves from us, not in a way that we deserve from the Lord. A clue is found in Colossians 1:10 which says, "Walk worthy of the Lord, to please him." But Hebrews 11:6 says, "Without faith it is impossible to please him." So the call to walk "worthy of the Lord" is at least a call to walk by faith.
But faith looks away from itself to the worth and ability and grace and strength of another. So walking "worthy of the Lord" would mean acting in a way that shows how worthy and able and gracious and strong the Lord is.
Another clue to this interpretation would be Matthew 3:8 where John the Baptist says, "Bear fruit worthy of (aksios) repentance." This surely does not mean: Act in a way that deserves repentance or merits repentance. Rather it assumes that repentance is there as something extremely valuable and calls us to act in a way that fits the value and nature of repentance. Thus the NASB translates it, "Bear fruit in keeping with repentance," and the RSV translates it, "Bear fruit that befits repentance."
So it is with the phrases "worthy of God" and "worthy of the Lord" and "worthy of the gospel" and "worthy of the calling." They mean: Act in a way that fits the great value and glorious nature of God and the gospel and your calling. And what fits with that great value? Faith. Above all things, faith and its fruit of love fits the worth of God and the gospel.
So think this way. NOT: I must have faith and love so as to be worth God's favor; BUT RATHER: God's favor is free and it is infinitely worth trusting. Walking worthy of that favor means walking by faith, because faith is the one thing that agrees with our bankruptcy and God's infinite "worth." Looking to God's infinite worth for our help and satisfaction is "walking worthy of God."
Wanting to walk ever more worthily of God with you,
By John Piper. © Desiring God. Website: desiringGod.org