"How can the saints in heaven hear us?"
I don’t know; I just know they do. I know this because the Bible says so:
Luke 15:7
I say unto you, that likewise joy shall be in heaven over one sinner that repenteth, more than over ninety and nine just persons, which need no repentance. (KJV)
The question you have to ask yourself is
“how do they know?”. Again, I don’t know, they just do. Add to this the fact that most repentence is
not auricular (spoken), and you have those in heaven knowing the hearts of men on earth.
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“Isn’t that an attribute of God alone?”**
No. Again, the Bible tells me it’s not:
Rev 5:8 And when he had taken the book, the four beasts and four and twenty elders fell down before the Lamb, having every one of them harps, and golden vials full of odours, which are the prayers of saints.
This depicts the elders in heaven delivering to God the prayers of the ‘holy ones’ (saints) on earth. How do they know? Aren’t most prayers silent?
1 Cor. 13:12 “Now I know in part; then I shall understand fully, even as I have been fully understood”
Again, I don’t know how, I just know that it is. They “fully understand”. I also don’t know how a toaster knows when to eject the bread, but I know it works. All that is certain is that it is not of their
own power by which they know what they do - it is by the power of God alone.
You may also consider Ananias and Sapphira from Acts 5. Did
they confess their sins to Peter? How did he know? God revealed their hearts to him. (Acts 5:4 “…Why have you conceived this thing in your heart?..”)
"Do they hear us when we pray to God? If we approach God in prayer, can we approach Him by Himself?"
Heb. 12:22-24 But you have approached Mount Zion, the city of the living God, the heavenly Jerusalem, and myriads of angels, and the assembly and church of the firstborn who have been enrolled in heaven, and God the judge of all, and spirits of righteous ones who have been made perfect, and Jesus, the mediator of a new covenant, and the sprinkled blood which speaks better than that of Abel.
It seems not. God is never alone. Even before creation, God was by His very nature (Trinity)
never alone.
Once you start to see heaven as a place of eternal unity with God, the idea that in unity all share to some degree the knowledge of God seems far more plausible.
Hope this helps.
God Bless,
RyanL