"But your iniquities have separated you from your God; And your sins have hidden His face from you, so that He will not hear." ~ Isaiah 59.2
In Isaiah's day the Israelites complained that God could not hear their prayers and petitions. They faced adversaries from without and troubles from within, but God did nothing to help them. Fasting was ordered and fervent prayers were offered in an unsuccessful attempt to stir Him. Grumbling and complaint rose ever louder against the Lord in those days. They cried out "Why have we fasted and You have not seen? Why have we afflicted our souls, and You take no notice?" (58.3) The perception was that He could not respond to their demands. The reality was that He would not.
For the believer, sin undealt with is a barrier in the relationship with God. Whether it is willful negligence or unknown oversight, sin that has yet to be repented of hinders the prayers and worship of the believer. In the Sermon on the Mount, Jesus made the point that a person should press the pause button when offering a sacrifice if he remembers an issue between himself and a brother (Matthew 5.23-26). In other words, if they sinned against another they were to make that relationship right by confessing their sin and asking forgiveness from the brother sinned against. Why? so the sacrifice would be accepted. The psalmist wrote, "If I regard iniquity in my heart, the Lord will not hear" (Psalm 66.18). Although it is not an issue of salvation for the believer, sin can separate us from the blessing, benefit, and protection of God as well as the relationship with God; however, the believer will never be separated from God Himself.
The unbeliever who refuses to acknowledge sin, repent and receive forgiveness will not only miss out on the blessing, benefit, and protection of God, but will be separated from God Himself! The only prayer the Lord will hear from the unbeliever is one of broken surrender in repentance and seeking the forgiveness He offers through Jesus Christ.
Believer, ask God to reveal any unknown and/or unrepented of sin. When the light of the Holy Spirit shines in the dark recesses of your soul be willing to confess, repent and ask forgiveness from God and anyone you might have sinned against. Then walk by faith in the joy of a restored relationship with your Father in heaven.
Unbeliever, confess, repent of, and ask forgiveness for your sin. Receive from Jesus Christ the cleansing that comes by faith through His shed blood and experience the new life given by the Holy Spirit. You, too, will then experience the joy of a relationship with the One who made and purchased you at His greatest expense.