Reasons not to pray
There are a number of reasons Christians may feel unable to pray. Guilt is one, trials another. There is however a universal medicine for the prayerless heart and that is a reminder of the character and glory of our Mediator in heaven, Jesus Christ our Great High Priest.
The medicine in four spoon fulls
The book of Hebrews encourages those who have drifted away to return; and it's chief inducement is to lay before the reader the glory of Jesus Christ, and most especially his ability to act as our sympathetic mediator. Here are four reasons we should pray without ceasing:
(1) Jesus was and is a real man like we are
Jesus was made like his brothers in every way. In his humanity he was, as Paul says "made in the likeness of sinful flesh". That does not mean he was a sinner, but it does mean he was a s close to us as it is possible to imagine - without sin. We are not to imagine that his divinity helped his humanity - so that he wasn't really a human being for he could call on his divinity in a fix. No, he was a real man, who lived a real human life, as we do. And gloriously, he remains a man in heaven now. Able to understand and be moved by our human frail condition. So you can pray knowing God understands what it is like to be a frail human being.
(2) Jesus suffered as we suffer
There is hardly a suffering - and certainly no category of suffering - that Jesus did not face. He experienced family pressures, work pressures, financial pressures, desertion, torture, pain, abandonment. In fact it was God's will to allow him to suffer so that he could walk in our shoes and become a sympathetic high priest. He knows what we are passing through - if not the exact experience, then the category. So you can pray knowing God in heaven understands.
(3) Jesus was tempted as we are tempted
(4) Jesus wrestled with God's will
In the Garden of Gethsemane Jesus faced an ugly future - death in all its manifest forms - and recoiled from it. He wrestled with the Father's will, but in the end submitted to it. When God asks us to do things that are difficult, we can know that he understands what it is like to wrestle with God's will.
The medicine for prayerlessness is to realise that we have in heaven someone who is able to sympathise with our weaknesses, and so to pray knowing we will be heard - no matter what we are passing through.