There is no grounds for any form of complaint or discontent being displayed in the life of the believer (really, for anyone). Consider Jesus Christ, how He did not open His mouth to complain (Isaiah 53:7), nor rejected the call and purpose of God for His life; but rather said to the Father, “not My will, but thine, be done” (Luke 22:42).
Jesus fulfilled His call with joy (Hebrews 12:2). Even to the point of death, Jesus was joyfully obedient and faithful. How can we who have received of the gift of God in Christ show any form of discontent in ANY circumstance, when Jesus freely gave / laid down His life for us, with joy.
Joy is a fruit that should never be lacking in the believer’s life, because “the joy of the Lord is our strength” (Nehemiah 8:10). To be without joy means you aren’t relying on the Lord’s strength. We should never be looking to ourselves, but rather, drawing from the joy of our Savior.
“These things have I spoken unto you, that my joy might remain in you, and that your joy might be full.” – John 15:11
“In His presence is fullness of joy” Psalms 16:11. When complaint and discontent arises, we must submit / subject ourselves to the will of God and not allow our fruit / seeds to be corrupted.
“But the fruit of the Spirit is love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance..” – Galatians 5:22