Prideful, materialistic and arrogant

If a person is a Christian, can they still be arrogant, materialistic and prideful? I was reading a blog of a person who recently came to faith in Jesus. I read the entire contents of one of his blog entries. It sounded like he definitely had a God encounter but many things which he  spoke about troubled me. He kept giving glory to the Trinity which was a bit odd to me. I guess it is no different than a person closing a prayer in the name of the Father, the Son and the Holy Spirit. It was obvious that he was new in the faith because he still spoke as an immature Christian. There were hints of arrogance in his speech as well as a mention of his  accomplishments in life as though he was the sole author of them. He referred to his possessions as "my stuff" vs God's stuff where he was merely the steward.

I was led to the blog by my unsaved sister-in-law who has no yet interest in becoming a Christian. She believes that Christianity is a cult. I have consistently prayed for her salvation. God is working on her heart. I haven't given up on her yet because the door is still open and she is still asking questions. We have had some great conversations. She has said some really untrue statements about God and Christianity but I have learned to allow her to say things because she truly doesn't really know anything about Christianity. She is still blind and lacks discernment. She does not have the Holy Spirit living in her. She wrongly believes that Christianity is a cult though she gave no evidence. She is led to believe things through what the world system has taught her and brainwashed her to believe. While the door is open and while it is still day I will actively engage her with questions to cause her to think and lead her to Christ. Lord use me up.