1 CORINTHIANS 12:3
"I want you to know that no one speaking by the spirit of God will curse Jesus, and no one can say JESUS IS LORD, except by the Holy Spirit."
All believer's should know for certain that Jesus Christ is the Lord God! We may not understand the trinity completely, but, we know that the Father is God, the Son is Jesus Christ and then we have the Holy Ghost. This is a core belief and is not subject to consideration. Just as you can not believe in seven out of the ten commandments, you can not have Jesus without having God or the spirit. In fact the proof of this truth for today can be tested. If anyone is professing a different Jesus or a different God or a different Spirit, test them and prove this concept. Ask them to say that they believe that Jesus Christ if the Lord God. They can not do it!
Although many people and among them believers use the name of Jesus Christ to curse others that is not the same as cursing Jesus. Using God's name in vain is equivalent to rejecting God and not believing in the Holy Spirit. That is what is meant by blaspheming the Holy Spirit. It is the unforgivable sin. If you reject Jesus, or God or the Holy Spirit you are committing blasphemy and it will be unforgivable. Your non acceptance is your choice and that choice will doom you to everlasting separation from God. Your sins will never be forgiven.
If we have the spirit of the Lord Jesus in us we can not curse, reject, or blaspheme Him. That is the comfort of having opened the door to your heart and allowing Jesus and the Holy Spirit to come and reside and dwell with you. Your sins are forgiven and you will be given eternal life. The other side of the equation is that if you have not accepted Jesus as the Lord of your life and received the Holy Spirit you will be forever separated from God the father, Jesus the Son and the Holy Spirit. In that condition you could never say that JESUS IS LORD! Can you say it?