The story is told of a simple Jew who was praying on Rosh Hashanah from the prayer book and was energetically reciting one of the esoteric piyutim (poems), whose meaning is difficult to decipher.
When he was asked if he knew what he was saying, he replied, “Of course! ‘Master of the universe, give me a livelihood!’ ”
Essentially, this Jew was right.
Prayer with such intent is certainly superior to the prayer of someone who is busy thinking how the name of the author appears in the initial letters of the stanzas, when he lived, and whether the piyut is constructed in a simple or complex form.
Knowing the meaning of the words is important–but only if it leads a person to a fiercely emotional attachment to God.
If not, the words are attached to another realm altogether and only interfere with prayer.
–Rabbi Adin Steinsaltz