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Does God hear all prayers made by Christians?
(NASB)1 John 5:14-15
This is the confidence which we have before Him, that, if we ask anything according to His will, He hears us.  And if we know
that He hears us in whatever
we ask, we know that we have the requests which we have asked from Him.
There are a number of points to consider here:
What does it mean to ask according to his will?
How do we get to the place where we have whatever we ask.
Most people ponder what it means to ask according to his will. Here are some examples of his will.
(ESV)1 Thessalonians 5:16-18
Rejoice always,  pray without ceasing,  give thanks in all circumstances; for this is the will of God in Christ Jesus for you.
(ESV)1 Peter 2:15-17
For this is the will of God, that by doing good you should put to silence the ignorance of foolish people.  Live as people who are free, not using your freedom as a cover-up for evil, but living as servants of God.  Honor everyone. Love the brotherhood. Fear God. Honor the emperor.
So according to a casual reading of that scripture one would conclude that there are only two possible outcones:
“We know that God does not hear sinners; but if anyone is God-fearing and does His will, He hears him.
We know many of the old testament prophets who certainly weren’t perfect yet God heard them. The question is then raised about what the phrase “God does not hear sinners” might actually mean. Especially if one believes in the often
(NASB)1 John 3:21-22
Beloved, if our heart does not condemn us, we have confidence before God;  and whatever we ask we receive from Him, because we keep His commandments and do the things that are pleasing in His sight.
The apostle John arrived at a place where he had 100% success in prayer. I think this unlikely that he had anything to do with sinless perfection. I have not met anyone who has stopped sinning altogether.
You ask and do not receive, because you ask with wrong motives, so that you may spend it on your pleasures.  You adulteresses, do you not know that friendship with the world is hostility toward God? Therefore whoever wishes to be a friend of the world makes himself an enemy of God.
Therefore we see the wrong motives were to be friends with the world. To seek the favour of men is to miss the blessing of God.
“How can you believe, when you receive glory from one another and you do not seek the glory that is from the one and only God?
“He who speaks from himself seeks his own glory; but He who is seeking the glory of the One who sent Him, He is true, and there is no unrighteousness in Him.
It is not good to eat much honey, nor is it glorious to seek one’s own glory.
We know that without faith it is impossible to please God.
And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him.
Behold, the LORD’S hand is not so short That it cannot save; Nor is His ear so dull That it cannot hear.  But your iniquities have made a separation between you and your God, And your sins have hidden His face from you so that He does not hear.