But if you have bitter jealousy and selfish ambition in your hearts, do not boast and be false to the truth. (ESV)
Knowledge is a dangerous thing. It is something that we are instructed to grow in. We are to pursue knowledge of the Word of God. We are to seek after Jesus Christ, growing in our knowledge of him. Knowledge, if used properly can help us to more effectively live our lives for Jesus Christ. If we used knowledge improperly we can destroy ourselves and those whom we come in contact with.
Let's take a look at the previous verse. It will help us to put today's verse in context.
 Who is wise and understanding among you? By his good conduct let him show his works in the meekness of wisdom. (ESV)
Those who are wise and understanding are to use what they have learned in meekness. Their good conduct will show that their heart is in the right place. In today's verse James offers a warning that if we have bitter jealousy and selfish ambition in our hearts we will be false to the truth. So, we see that proper gaining of knowledge must be accompanied by a heart that is properly motivated.
Have you ever met someone who seems to know a lot of the Bible, but you would never want to spend five minutes with them in a social context? There are people who use Scripture so that they have a weapon to fire at someone whom they disagree with. This is a person who is motivated by jealousy and selfish ambition.
Take a careful look at yourself. Do you pursue knowledge? You should be pursuing knowledge! Now look at little deeper. Is your pursuit of knowledge based on a humble desire to be more like Christ? Or is your pursuit of knowledge based on a desire to know more than someone else? Do you have the wrong ambition for pursuing the truth.
What we know can be used to bless others or tear them apart. Ask the Lord to show you your heart. If there are areas where your heart needs to change he will gently heal you and help you. Seek him today.