The Jesus prayer comes directly from the Bible. In various encounters with Jesus people used the phrase, 'Have mercy on me'. What an amazing thing to say to somebody - because it implies that the speaker truly believes that the hearer has the capacity and the will to look on them with compassion and acceptance - yes, and even forgiveness.
Below is a story that Jesus told about two men:
From Luke 18
He also told this parable to some who trusted in themselves that they were righteous and regarded others with contempt: 'Two men went up to the temple to pray, one a Pharisee and the other a tax-collector. The Pharisee, standing by himself, was praying thus, “God, I thank you that I am not like other people: thieves, rogues, adulterers, or even like this tax-collector. I fast twice a week; I give a tenth of all my income.” But the tax-collector, standing far off, would not even look up to heaven, but was beating his breast and saying, “God, be merciful to me, a sinner!” I tell you, this man went down to his home justified rather than the other; for all who exalt themselves will be humbled, but all who humble themselves will be exalted.’
In the story the tax collector says, "God, be merciful to me, a sinner."
Words that we all need to say.
The Jesus Prayer, also called the Prayer of the Heart, is a very short, simple prayer. The classical form of the Jesus prayer is:
Lord Jesus Christ, Son of God, have mercy on me, a sinner.
Shorter alternatives include:
Lord Jesus Christ, have mercy on me.
Lord Jesus, have mercy.
There are different ways that we can use the Jesus Prayer:
In our personal prayer time it can be used as a form of steadying, repetitive prayer to still our hearts and bring us to a place of greater communion with God.
Here is a useful description of how it might be used that way from www.prayerguide.org.uk
As you pray the prayer, simply recite it over and over again, and you will discover three levels of prayer, first described by the 19th C. Russian spiritual teacher, Theophan. The prayer begins as words, then as we recite it further, we move onto pray the prayer as our own, owning the thoughts and expression of the prayer. Finally, our hearts take over the prayer, where the prayer is no longer a series of words and concepts, but gives way to a touching of our Spirit with God's Spirit.
If you use this prayer (and some may find this sort of prayer simply not for them) then if you are alone you might try saying the prayer out loud rather than silently. It can be a way of helping with distracting thoughts.
Jesus taught us to ask in his name:
"Hitherto you have asked nothing in My Name; ask and you will receive, that your joy may be full." John 16:23
When we use the Jesus Prayer we are asking directly in his name, acknowledging in the first part the Lordship and divinity of Christ and in the second our own need and impotence.
May God bless you as you pray.