Can Christians struggle with impure thoughts?

Yes they can. Remember David and Bathsheba?

One evening David got up from his bed and walked around on the roof of the palace. From the roof he saw a woman bathing. The woman was very beautiful, and David sent someone to find out about her. 2 Samuel 11:2-3a

You know the story. David ended up having Bathsheba’s husband killed so he could have her as his wife. This is the same man who years earlier wrote in the book of Psalm praises to God. We are all born into a sin nature and as Christians we still wrestle with that sin nature. Most (if not all) Christians are ashamed and saddened at the thoughts that sometimes come into our minds. The best thing is not to become obsessed with those thoughts and to clear our minds when they do occur. Our priority in life is to please an almighty God with what we do, say and think.

So I say, live by the Spirit and you will not gratify the desires of the sinful nature. For the sinful nature desires what is contrary to the Spirit, and the Spirit what is contrary to the sinful nature. They are in conflict with each other, so that you do not do what you want.

Galatians 5:16-17

Treat impure thoughts as they are, sin. You need to repent and ask Jesus to forgive those sins when they happen. This asking Jesus to forgive you is not the same forgiveness you asked for to go to heaven, but is a sin that prevents an ongoing relationship with Christ. He will forgive you and your relationship will be stronger. Asking Jesus to help and reading and thinking about Bible verses that focus on the greatness of God, will help our minds stay on thoughts that will please God. Recognize that there is a battle in all of us, Satan on one side and God on the other.

Finally, be strong in the Lord and in His mighty power. Put on the full armor of God so that you can take your stand against the devil’s schemes. For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms.

Ephesians 6:10-12

In this life we will never be free from impure thoughts. We can, however, control their influence on our lives. With disciplined resistance we can rid ourselves from the habitual, willful sin.