2 Peter 1:8 says,
For if these qualities [knowledge, moral excellence, self-control, kindness, godliness, …] are yours and are increasing, they render you neither useless nor unfruitful in the true knowledge of our Lord Jesus Christ.
All Christians should be working to increase in these areas so we can be useful and fruitful in service to our Lord. While we will never be perfect in this life, neither should we be satisfied with being immature in our faith. We should not desire not be useless or unfruitful.
If we look at this verse in its context, we can see the emphasis that Peter places on both proper knowledge (orthodoxy) and proper actions that come from that knowledge (orthopraxy).
Grace and peace be multiplied to you in the knowledge of God and of Jesus our Lord; seeing that His divine power has granted to us everything pertaining to life and godliness, through the true knowledge of Him who called us by His own glory and excellence. For by these He has granted to us His precious and magnificent promises, so that by them you may become partakers of the divine nature, having escaped the corruption that is in the world by lust. Now for this very reason also, applying all diligence, in your faith supply moral excellence, and in your moral excellence, knowledge, and in your knowledge, self-control, and in your self-control, perseverance, and in your perseverance, godliness, and in your godliness, brotherly kindness, and in your brotherly kindness, love. For if these qualities are yours and are increasing, they render you neither useless nor unfruitful in the true knowledge of our Lord Jesus Christ. For he who lacks these qualities is blind or short-sighted, having forgotten his purification from his former sins. Therefore, brethren, be all the more diligent to make certain about His calling and choosing you; for as long as you practice these things, you will never stumble; for in this way the entrance into the eternal kingdom of our Lord and Savior Jesus Christ will be abundantly supplied to you.
Without proper knowledge of God and his Will, we cannot know what to believe and how to act. Without proper belief and action, that knowledge of God is useless and unfruitful. There is a balance between dead doctrine (knowledge only) and false faith and works (action only).