8 Now they heard the sound of the Lord God walking in the garden in the [a]cool of the day, and the man and his wife hid themselves from the presence of the Lord God among the trees of the garden. 9 Then the Lord God called to the man, and said to him, “Where are you?” 10 He said, “I heard the sound of You in the garden, and I was afraid because I was naked; so I hid myself.” 11 And He said, “Who told you that you were naked? Have you eaten from the tree from which I commanded you not to eat?” Genesis 3:8-11, NASV
Very early on in Genesis, we see the story in Genesis 3 of the fall of man. Before this time, possibly for a long time, God would walk with Adam and Eve in the garden and have fellowship with them. But, this evening Adam and Eve for the first time ever hide from God. God asks them "Where are you?" That's an important question and we have to realize that God is not asking this to get information because God knows everything. He is even at this point giving them a chance to reveal to Him what they did and repent of it. You notice that sin immediately brings about shame and separation from God.
Even in the life of the believer, sin can cause separation from God and difficulties in the fellowship of a believer and God. This is because God is light and in Him there is no darkness at all (1 John 1:5). Most of the world doesn't come to God even to this day because they love the darkness rather than the light for their deeds are evil. Likewise, a believer can get caught up in sin and get out of fellowship with God and then have difficulty with hearing from God.
It is easy, in this day and time to get your eyes off of Christ and on the world. Idols come in all shapes and sizes including things like money, jobs, a hunger for power or control or selfishness or greed. I feel like one of the biggest obstacles that mankind has to overcome is simple pride. It requires humility to humble yourself before God and realize you can't make it to heaven on your own effort.
There are many places in the Bible that warn us that if we are walking out of fellowship with God that our prayers could be hindered. Several times in places such as Ps 66:18; Proverbs 1:28, Isaiah 59:2, Zech 7:13, 1 Peter 3:12, Isaiah 1:15. The key is what the Bible refers to as repentance. Repentance means a turning away from self and selfish desires and turning to God. It begins by confession of sin. Every great revival in the history of the church began when people started to repent.
A passage that people love to quote is found in 2 Chronicles 7:14 "If my people, who are called by my name, will humble themselves and pray and seek My face and turn from their wicked ways, then will I hear from heaven and will forgive their sin and will heal their land." Did you notice that this promise is conditional? It says that "my people" are to humble themselves, seek God's face and turn from their wicked ways. That is a good summary of the idea of repentance to humble themselves, seek Him, turn from wickedness. This takes us from hiding from God to seeking Him out. It takes us from shame to mercy, from alienation to reconciliation, from separation to fellowship.