Mariah Carey's hit song "One Sweet Day" includes the line: "And I know you're shining down on me from heaven / Like so many friends we've lost along the way."

However, while the idea that saints in heaven are looking down on their loved ones below is certainly comforting, there are a few things that one should keep in mind before buying into it completely, says theologian John Piper, who in recent blog post, shares five thoughts on subject.

First, we don't know to what extent saints might be allowed to see and know all that goes on on earth, says Piper: "There is at least one passage of Scripture that some writers would interpret in a way that makes it quite clear that they do know what is going on," he says. "I think that I would not stake my life on a position on this, because I don't know for sure."

Second, the Bible says that saints have been perfected in heaven (Hebrews 12:23). So, if they able to see, they will no longer view the world through old, imperfect lenses.

"[They] will see and understand and assess all things in a perfectly spiritual way that takes into account everything they need to know in order to make sense of it and to keep from making any mistakes," he explains. "And so, they will not in the least doubt the goodness of God in what they see or the wisdom of God in what they see."

Piper points to Hebrews 12:1 as one verse that suggests the saints in heaven are, in fact, witnessing the race that we are running on earth. He explains, "It is as though the saints finish their marathon at their death. Then they come around and stand on the side of the racetrack and watch us. And we are supposed to take heart from that because, in essence, they would be saying: Hang in there. Trust God. You can do this. We made it. You can make it, too. And I find that very, very encouraging."

However, it's important to be remember that it can be "very dangerous for the health of our faith" to think too much about the saints above, says Piper.

"It has led many people, millions I fear, to look to the saints and to Mary in their longing for help, rather than focusing on Christ and the throne of grace that he has opened to us," he says. "Christ is the one mediator between God and man. And the New Testament does not encourage us to make the saints or Mary into mediators as we seek God's help."

Finally, the theologian cautions against sentimentalism and the common idea that everybody that dies goes to heaven. He points to Matthew 7:22-23, which reads, "On that day many will say to me, 'Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?' And then will I declare to them, 'I never knew you; depart from me, you workers of lawlessness'."

"And that is a warning not just for ourselves, lest we deceive ourselves into thinking we are following Christ when we are not," Piper concludes. "It is also a warning that we not be sentimental as though everybody who is a good person who died is going to be in heaven."

Ultimately, Piper says it's important to remember that "if saints see you at all they are cheering you on to endure every hardship by encouraging you to focus on Christ."

In an earlier blog post, Piper said that it's not necessarily helpful to speculate about the state of our deceased loved ones: "I want to say that the comforts that the Word of God gives to those of us who have lost Christian loved ones are so massive and so glorious it is a shame that anyone would resort to speculation to find comfort," he wrote.

He added that Christians on earth simply must trust what we are told in the Bible about the happiness of the saints in heaven: [All] speculation about such things for the sake of strengthening our souls, is a spiritual detour off the main highway of God's blessing and comfort and strength and hope. The highway is what he has revealed in the Bible and it is glorious beyond words," he concluded.