That's an easy one...
Now before I give you chapter & verse, a few qualifiers are in order:
(a) I am not Roman Catholic;
(b) I believe prayer is reserved as the Bible depicts it -- as to be directed to God alone;
(c) The apostle Paul's counsel to Timothy about Jesus being the ONLY MEDIATOR is downright ignored by Catholic doctrinaires & Catholics who advocate praying to entities beyond God;
and (d) AMorePerfectUnion's first post on this thread is a great synopsis of what's wrong with those who argue from silence on this whole issue.
But, having said that, yes...departed saints can -- and do indeed -- lobby our Lord in heaven...and I base that on this passage:
Revelation 6: 9 When he opened the fifth seal, I saw under the altar the souls of those who had been slain because of the word of God and the testimony they had maintained. 10 They called out in a loud voice, “How long, Sovereign Lord, holy and true, until you judge the inhabitants of the earth and avenge our blood?” 11 Then each of them was given a white robe, and they were told to wait a little longer, until the full number of their fellow servants, their brothers and sisters, were killed just as they had been.
So...Cynical...go ahead & be cynical...but your tone toward Catholics on this particular matter needs a bit more humility...asking the question in a manner that assumes topical "MIA" status from the Bible...yet only serves to reveal your own Biblical ignorance instead.
The question is more, "Why should anybody -- especially Catholics -- assume that departed saints are omniscient or neo-omniscient in being able to tune in to all those prayers directed to God?"
And, secondly, "Why would anybody assume that a 'prayer' to a departed saint or to Mary would somehow 'trump' a prayer directed to the Son of God? Why does He get 'semi-mediator' status in their eyes?"
That was a nice try Colofornian but there’s several errors in your attempt to correct me. First of all my question was “So show me from scripture where those who passed from this life after Christ’s resurrection have an active role in what goes on here on earth.” The verse from Revelation does not show that they are in any way active in what is going on here one earth. They are active in what is going on in heaven. Read the passage again. They aren’t carrying any prayers from anyone one earth. They are asking when God will avenge their deaths. They are told to wait until “the full number” of those who will be killed during the Tribulation have been. Surely you don’t equate their request for vengeance to what the Catholics refer to as saints do you?
Second problem with your attempt is that those saints are Tribulation saints. Those that were killed for not taking the number of the beast during the Tribulation. The church, the body of Christ, has long left the earth by that point and are already in their white robes.
So please don’t accuse me of ignorance when the verse you used clearly does not answer the question I asked.