Why this question is a non-gospel-centered question: The only reason people struggle with this is because Christians (most of the ones I know) only want to worry about things that affect their salvation. The question behind the question could be:
- “If I’m already justified, why should I worry about whether or not the Holy Spirit is grieved?” To paraphrase John Calvin, the displeasure of God should always be more of a motivating factor for obedience than the threat of punishment. We believe the gospel because God is lovely, not because we fear hell.
- or “Why would God let anyone into heaven who displeases him?” That seems to miss one of the great truths of the gospel, that God justifies the ungodly. Those who once were enemies, and those who, after being reconciled, continually stumble in many ways and grieve the Holy Spirit, are still allowed to see the Kingdom of God because of, and only because of, the righteousness of Christ!
- or “How is it not a contradiction that God is pleased and displeased by the same human being?” That seems to miss one of the great truths of justification. That is not a contradiction in the same way it is not a contradiction that God is well-pleased with, and at the same time was pleased to crush, the same Person, namely, His Son.
I hope that helps in understanding a bit more of what it means to be gospel-centered. Might there be any other questions behind the question I might be missing?