I have been trying to understand a teaching about the Holy Spirit. I am talking about person who is living a very sinful life all that time between. Thank you for your answer. You have asked quite a difficult question, and one that receives different answers among Oneness Pentecostals. The answer hinges on many other theological positions.
Most Pentecostals are Arminian.
Also, being an Arminian, I do believe that it is possible to lose one's salvation. However, I firmly believe that the Scripture teaches that salvation is forfeited because of a lack of faith, not because of personal struggles with sin. We may be saints, but our sin nature was not eradicated in the new birth. As long as we possess this sin nature, we will still struggle with sin. Ultimately, however, if we truly have faith we will allow God to continually sanctify us, and thus become more and more holy as we are conformed to His image.