A common objection to the theology of Saintly intercession is that the Saints can't "hear" us. While there is a theological argument to be made that they, in fact, can hear us, I think that's going to be a separate post. For now, I'd like to look at the biblical case for the Saints being aware of our prayers, or at the very least, aware of what is happening on this side of eternity.
Rejoicing in Heaven
In the parables of the lost sheep and lost coin, Jesus concludes by saying that when a sinner on earth repents, there is joy in heaven.
"What man of you, having a hundred sheep, if he loses one of them, does not leave the ninety-nine in the wilderness, and go after the one which is lost until he finds it? And when he has found it, he lays it on his shoulders, rejoicing. And when he comes home, he calls together his friends and neighbors, saying to them, ‘Rejoice with me, for I have found my sheep which was lost!’ I say to you that likewise there will be more joy in heaven over one sinner who repents than over ninety-nine just persons who need no repentance."Or what woman, having ten silver coins, if she loses one coin, does not light a lamp, sweep the house, and search carefully until she finds it? And when she has found it, she calls her friends and neighbors together, saying, ‘Rejoice with me, for I have found the piece which I lost!’ Likewise, I say to you, there is joy in the presence of the angels of God over one sinner who repents."---Luke 15:4-10, emphasis added
If such joy in heaven is a response to the happenings on earth, it must mean that in some sense such events are knowable by those in heaven.
The rejoicing in heaven is paralleled with the rejoicing of the father with the return of the prodigal son. Just as he celebrates his son's return, so too do the angels in heaven rejoice when a lost sinner comes home.
A Cloud of Witnesses
After Hebrews 11, where Paul(?) lists the so-called "hall of faith", he states that we are surrounded by "so great a cloud of witnesses."
Therefore we also, since we are surrounded by so great a cloud of witnesses, let us lay aside every weight, and the sin which so easily ensnares us, and let us run with endurance the race that is set before us, looking unto Jesus, the author and finisher of our faith...---Hebrews 12:1-2a
This directly implies that those on earth, who are "running the race" - a metaphorical reference to the Greco-Roman Hippodrome/marathon race - are observed by "witnesses" (lit. μάρτυς, martyrs). Paul's(?) exhortation uses this "cloud of witnesses" as motivation for us to finish the race well, as though they are cheering us on. Given such usage, it seems almost dishonest to suggest that he is speaking of these Saints as witnessing us merely as a metaphor.
As a side note, it is interesting that even as we are surrounded by these Saints, cheering us on, our focus is to be on Christ, as the text says. So much for the Saints taking our focus away from Christ, as the objection often goes.
Even more so, when we consider that in just a few verses, Paul(?) speaks again of those in heaven as part of the heavenly hosts:
But you have come to Mount Zion and to the city of the living God, the heavenly Jerusalem, to an innumerable company of angels, to the general assembly and church of the firstborn who are registered in heaven, to God the Judge of all, to the spirits of just men made perfect, to Jesus the Mediator of the new covenant, and to the blood of sprinkling that speaks better things than that of Abel.---Hebrews 12:22-24
Here we see described that "cloud of witnesses". It is a collection of those angels spoken of elsewhere, but they are accompanied by the Church --the just men made perfect--- and led by Christ, who is the mediator of the New Covenant. Another interesting note here is that this cloud of witnesses, including the Saints, in no way takes away that Christ is the mediator of the New Covenant (an objection to be tackled in a later article).
Maccabees, Jeremiah, and Elijah
Perhaps less convincing to Protestant objectors, but still worth noting is the instance of praying to Saints in Maccabees.
What he saw was this: Onias, who had been high priest, a noble and good man, of modest bearing and gentle manner, one who spoke fittingly and had been trained from childhood in all that belongs to excellence, was praying with outstretched hands for the whole body of the Jews. Then in the same fashion another appeared, distinguished by his gray hair and dignity, and of marvelous majesty and authority. And Onias spoke, saying, "This is a man who loves the family of Israel and prays much for the people and the holy city—Jeremiah, the prophet of God." Jeremiah stretched out his right hand and gave to Judas a golden sword, and as he gave it he addressed him thus: "Take this holy sword, a gift from God, with which you will strike down your adversaries."---2 Maccabees 15:12-16
In order to encourage his troops, Maccabeus conveys to them a vision of two Saints: Onias, a former High Priest, and Jeremiah the Prophet.
In this vision, both men are said to be praying for the Jews (vv. 12,14). This is significant, since both men at this time were dead, yet they are both interceding for the living.
Generally, those who would object to prayers to the Saints and praying for the departed would also object to the canonicity of the books of Maccabees. However, the books of Maccabees contain history which is celebrated at Hanukkah, a celebration in which Jesus joined (John 10:22), as was prescribed for the Jews in 1 Mac 4:59.
Lastly, it seems as though the practice of petitioning the Saints was at least a known practice for first century Jews. It was at least common enough for Jews to mistake Jesus for making such a petition:
And at the ninth hour Jesus cried out with a loud voice, saying, "Eloi, Eloi, lama sabachthani?" which is translated, "My God, My God, why have You forsaken Me?"Some of those who stood by, when they heard that, said, "Look, He is calling for Elijah!"---Mark 15:34-35, cf. Matthew 27:46-47
The bystanders of the crucifixion assumed Jesus was calling out to Elijah when they heard him shout "Eloi". While they mistakenly assumed this, the fact that speaking to the dead in such a way wasn't seen as abnormal, and the fact that their first assumption upon hearing "Elijah" was to conclude that Jesus was trying to call out to - or petitioning - a dead saint, speaks at the very least to the possible presence of the practice during the time of Christ. And given that the passage in Maccabees (above) shows early Jewish literature attesting to such petitions, it is not unlikely that the Jews that lived at Jesus' time would have been familiar with this kind of practice.