Can a Christian be miserable, and what does misery indicate about their fellowship with the Lord?
There is no room for miserable Christians. If believers are miserable, that misery indicates they are out of fellowship with the Lord and are out in the world where they should not be. God instead wants His children well taught, grounded, and enjoying the joyous life He provides.
Les teaches that God does not want a bunch of ignorant believers in the Body. He wants every child of His to be well taught, well instructed, grounded, and to enjoy the faith. Les says there is no room for miserable Christians; if they are miserable, they are out of fellowship with the Lord and out in the world where they should not be. By contrast, it is a joyous life, and God wants it to be that way. The surrounding verses in Colossians 3 call believers to let the peace of God rule in their hearts, to be thankful, and to let the Word of Christ dwell in them richly in all wisdom.
Let the word of Christ dwell in you richly in all wisdom; teaching and admonishing one another in psalms and hymns and spiritual songs, singing with grace in your hearts to the Lord.