Pope Shenouda III
Conditions of the acceptable prayer and exercises in prayer
Not each prayer is acceptable because not each prayer is a PRAYER.
The prayer of the proud Pharisee was not acceptable like the prayer of the contrite tax collector, who returned to his house forgiven (Lk18:14). The same with the prayer of those whose hands are full of blood. The Lord said about them, “When you spread out your hands, I will hide My eyes from you; Even though you make many prayers, I will not hear” (Is 1:15 ). And also the prayer of the hypocrites (Mt 6), and those who for a pretence make long prayers (Mt 23:14).
You might pray a prayer and one of the twenty four elders would proceed and take it in his golden censor and present it to God, a sweet aroma of incense... (Rev 5:8). While another person would pray all day long and the angels would wonder at him, as none of his prayers ascended!