Eph 4:30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
First things first, let's read the verse in it's context
Eph 4:29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
31 Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:
32 And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you
So, In order to understand Eph 4:30 you need to read it in its context. What is the tone of the surrounding verses?
What exactly was Paul teaching on there?
One way to get clarity about the context of a text is to remove the particular verse and read the surrounding verses without it first and see what they are saying then insert it back again and read everything together.
Now let's do that for this text
Eph 4:29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
31 Let all bitterness, and wrath, and anger, and clamour, and evil speaking, be put away from you, with all malice:
32 And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you
After reading without verse 30 what is obvious about the context?
Walking in love!
Paul was teaching believers to walk in love towards other believers
He talks about not giving room for corrupt communication, bitterness, wrath, anger, clamour, evil speaking and malice
Says we should put away all these
Don't be found saying stuff that will hurt your brother out of anger
Then instructs us to instead be kind to one another, tenderhearted, forgiving one another for Christ's sake
Don't react from anger and hurt your brother with your words, rather be quick to forgive just as Christ has forgiven us
So, grieving the Holy spirit is directly connected to how we treat other believers who house the Holy spirit
When I grieve my brother by speaking evil of him and speaking words which do not minister grace to him I am grieving the Holy spirit also
Grieving my brother is grieving the Holy spirit
And grieving the Holy spirit is the same as grieving my brother
Now let's see
Eph 4:29 Let no corrupt communication proceed out of your mouth, but that which is good to the use of edifying, that it may minister grace unto the hearers.
30 And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption.
And... (That is) grieve not the holy spirit
And grieve not the holy spirit
How?
When I allow my communication to grieve my brother instead of edifying him
Meaning if my communication doesn't minister grace to my hearer (my brother who is sealed with the spirit just as I am) I grieve the spirit in grieving my brother
So grieving the Holy spirit has nothing to do with losing salvation or breaking fellowship with God as some have taught
Clear now?
You are blessed!