“When he opened the fifth seal, I saw under the altar the souls of those who had been slain for the word of God and for the witness they had borne. They cried out with a loud voice, ‘O Sovereign Lord, holy and true, how long before you will judge and avenge our blood on those who dwell on the earth?'” (ESV – Read the chapter)
This verse has long been really encouraging to me during times of loss. We have to be careful crafting doctrines from a single verse, but the picture John paints here seems to suggest pretty clearly (especially when paired with Jesus’s parable of the rich man and Lazarus in Luke 16) that those who have died before us are in some sense aware of what is happening here on earth. They may be dead and gone, but they are still somehow able to see and know what’s going on here.
We are not given any clues as to how this works or what it looks like and so we cannot confidently go much further than this, but if you have lost a loved one, I think it not inappropriate to be comforted by the thought that he or she still sees and knows what you are doing.