Ephesians 4:30-32

And do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption.

(v30, NIV)

What does it mean to grieve the Holy Spirit? Well, first of all, these things Paul is discussing give us insight in how to or how to not grieve the Holy Spirit. Speaking falsehood, allowing anger to swell within us, stealing and corrupting talk are things that will cause us to grieve the Holy Spirit. On the whole, sin and engaging in sinful acts are what cause us to grieve the Holy Spirit.

And you also were included in Christ when you heard the word of truth, the gospel of your salvation. Having believed, you were marked in him with a seal, the promised Holy Spirit,

(Ephesians 1:13, NIV)

Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own;

(1 Corinthians 6:19, NIV)

The Holy Spirit is given to us by God. When we receive the Holy Spirit, the Holy Spirit dwells in us. Our body is a temple of the Holy Spirit. We are not our own. We are owned by God. The Holy Spirit is a seal marking us as God's. When we act as if we are not owned by God, we grieve the Holy Spirit, who acts as a seal to mark God's ownership. Sin is in direct opposition to the Holy Spirit. Our sin hinders the work of the Holy Spirit in us and through us. So, a hindering of the Holy Spirit grieves the Holy Spirit.

Get rid of all bitterness, rage and anger, brawling and slander, along with every form of malice. Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you.

(v31-32, NIV)

We aren't to be bitter or angry. Of course it is possible to be angry and not sin, but anger often leads to sin. That is why we are instructed by Paul to not let the sun go down on our anger. We should simply do away with anger and things of that nature. This is all part of putting off our old self and putting on our new self. We should learn kindness, compassion and forgiveness in order to apply them to others. In fact, we must forgive one another. It was in Christ that God forgave us. If we are forgiven, how can we not forgive others?