How do we know that Christians should not complain?

In Philippians 2:14, the Apostle Paul explicitly instructs believers to perform all tasks without murmuring or disputing. This call to a positive attitude in service underscores the doctrine that our actions should reflect our identity as children of God. Complaining often reveals a lack of trust in God's providence and His good purposes for our lives. By avoiding murmuring, Christians can demonstrate their belief in the sovereignty of God and become witnesses of His grace to the world around them. Moreover, as they serve without complaint, they exhibit the character of Christ, who endured suffering without retaliation.