Matthew 6:34 says not to worry about tomorrow. How can we tell if worry becomes sinful?
“Worry” comes from the Greek term merimnao, which has two definitions: “to be anxious, to be troubled with cares” and “to care for, look out for (a things), to seek to promote one’s interests, caring or providing for.” The context of the Matthew passage shows that worry and anxiety over obtaining the necessities of life is the definition Jesus had in mind (Matt. 6:25-34). On the other hand, the definition of merimnao which has to due with “caring or providing for” is used to describe the responsibilities spouses have towards each other (1 Cor. 7:33-34) and Christian brethren have towards each other (1 Cor. 12:25; Phil. 2:20). A derivative of this Greek term was used by Paul to describe his “care” or “anxiety” (depending on the translation) “for all the churches” (2 Cor. 11:28). So there is a type of care and concern which is perfectly acceptable to God.
One commentator said that merimnao originally meant “distracted.” Jesus used this Greek term to describe Martha, who was “anxious and troubled about many things” to the point that she failed to “choose the good portion” and recognize what was truly important (Luke 10:38-42). None of us are immune from worry and anxiety. Yet from this we gather that worry becomes sinful when it distracts us from “setting our minds on things that are above, not on things that are on earth” (Col. 3:1-2), as it did with Martha.
Paul also used this Greek term to command us not to be “anxious about anything,” but instead to take everything to God in prayer which would result in the incomprehensible peace of God “guarding your hearts and your minds in Christ Jesus” (Phil. 4:6-7). Thus, one could conclude worry becomes sinful when we fail to bring our cares and concerns to God and thus fail to receive the peace which would guard our hearts and minds (cf. 1 Pet. 5:7).
Finally, the context of Matthew 6:34 shows that worrying over obtaining and keeping the necessities of life such as food and clothing indicates a weak faith (v. 30) and a worldly rather than spiritual mindset (v. 32). Christ would rather us “seek first the kingdom of God and his righteousness,” trusting that God will provide what we need (v. 33). Part of seeking first God’s kingdom and righteousness is being willing to work for a living to the best of one’s ability (2 Thess. 3:7-12; Col. 3:23), and also to allow others to help you in your time of need (Gal. 2:10; 6:2, 10; Matt. 25:31-46). Worry would become sinful when we allow it to be the reason for an unrepentantly weak faith, a mindset that is more similar to the world than God would have us, and/or the result of not seeking God’s will as one’s top priority.