Wesley L. Duewel: "Prayerlessness is also a sin against your own spiritual life. You cannot grow in grace when you neglect prayer.
You cannot develop a close walk with Jesus if you do not frequently commune with Him. You cannot share His heartbeat if you seldom intercede with Him.
Prayerlessness robs you of the consciousness of the near presence of Jesus. It robs you of the awareness of the smile on His face, of the blessedness of listening to His voice.
It robs you of the touch of his hand upon you and of much of His guidance. It robs you of His power.
Prayerlessness is all the more serious sin against yourself, since prayer is so blessedly simple. All you need to do to learn to pray is to pray.
It is so spiritually natural that new Christians almost begin to pray without being taught. Even little children can easily learn a very real, personal and satisfying prayer life as they talk to Jesus.
A Sin Against God
We may call prayerlessness a weakness, being so busy and preoccupied that we neglect what we know we should do. We may make many excuses, but God calls it disobedience. That is sin against God.
Prayerlessness is not only a direct sin against others, it is a direct sin against God Himself (1 Sam. 12:23). Jesus told us that we 'should always pray and not give up' (Luke 18:1.
Forsyth has said that for the Christian, 'the worst sin is prayerlessness.' (Bloesch, Struggle of Prayer, p.132). Why? Because it shows our indifference and disobedience to God.
Prayerlessness is an evidence of what our attitude is to
God. It is a kind of unfaithfulness and lovelessness.
(Murry, Ministry of Intercession, p. 24).
Our relation with God is not what it should be if we do not love him enough to find time to get alone and listen and talk to Him. Prayerlessness proclaims to God and to Satan that our relation to Jesus is not very loving and close.
Adequate relation to Jesus always includes prayer—both the desire and the actual practice."
(Google image and my emphasis added)