The Jesus Prayer has its origin in this (todays) parable. The text of the prayer is simple: “Lord Jesus Christ, (Son of God) have mercy on me, a sinner”. Although prayed since the sixth century, the modern technique associated with this prayer - controlled breathing and mantra-like repetitions – probably didn’t come into use until the fourteenth century. Like any prayer, the point isn’t to perfect the technique but to find the right spirit. The tax collector in the parable had the right spirit, even if he couldn’t imagine the technique that historywould form around his prayer. He simply bowed his head, acknowledged his sins, and counted on God’s mercy. The Pharisee, who had more style and undoubtedly greater technique, gave himself over to self-celebration, reporting his good deeds in the event God might have missed them. In the process, he missed the heart of prayer, which is humility. The lesson on prayer is simple. Pray however you want, but be sure of two things: that you DO pray, and that your heart is invested in your prayer. (Source: GPBS eNews) Bishop Kallistos Ware says that if we pray the Jesus Prayer for short periods, ten or fifteen minutes at the beginning, then there is no problem matching the words of the prayer to our breath. We are to breath naturally, without playing with the rhythm of the breath. On the inhale, we can say, "Lord Jesus Christ, Son of God." On the exhale, we can say, "have mercy on me, a sinner." We are to breath and pray slowly and reverently and attentively. ........ We don't say the Jesus Prayer, or enter wordless contemplation, to get "some benefit." We don't pray to reduce our stress, or strengthen our immune system, or lose weight, or add years to our life. On the contrary, we enter prayer to follow Christ, to become open to Him. His way is the Way of the Cross.
(Source: https://www.svots.edu/saying-jesus-prayer