Post #151357 explains both parts.
Both are true. Christians have their hope and faith in Christ and they continuously struggle against the sin in their life. We know the Apostle Paul was a Christian. We know also that he continued to have sin in his life due to the weakness of his flesh, as he told us. Again see how Paul puts it.
“For we know that the law is spiritual: but I am carnal, sold under sin. For that which I do I allow not: for what I would, that do I not; but what I hate, that do I. If then I do that which I would not, I consent unto the law that it is good.
Now then it is no more I that do it, but sin that dwelleth in me. For I know that in me (that is, in my flesh,) dwelleth no good thing: for to will is present with me; but how to perform that which is good I find not. For the good that I would I do not: but the evil which I would not, that I do. Now if I do that I would not,
it is no more I that do it, but sin that dwelleth in me. I find then a law, that, when I would do good, evil is present with me. For I delight in the law of God after the inward man: But I see another law in my members, warring against the law of my mind, and bringing me into captivity to the law of sin which is in my members. O wretched man that I am! who shall deliver me from the body of this death? I thank God through Jesus Christ our Lord. So then with the mind I myself serve the law of God; but with the flesh the law of sin.”
Romans 7:14-25 KJV
https://www.bible.com/1/rom.7.14-25.kjv
He says “ it is no more I that do it”. So, it is in this sense that Christians no longer sin. It’s all laid out right there.