God said to Noah, "Enter ... into the ark" (Genesis 7:1).
The Hebrew word for ark, teivah, has two meanings: it can mean "an ark," and it can also mean "a word." In the above verse, the latter meaning tells us that God instructed Noah to "enter into the word." Rabbi Moshe of Kobrin expounded on this theme, explaining that when we pray, we should "enter into the words," i.e. totally immerse ourselves into each word of prayer, as though the word is encompassing us.
A listener once asked him: "How can a big human being possibly enter into a little word?" Rabbi Moshe answered, "People who consider themselves bigger than the word are not the kind of person we are talking about."
The Talmud states that people's prayers are not accepted unless they efface themselves before God (Sotah 5a). God abhors those who are egotistical, and therefore the prayers of a vain person are not likely to be received favorably.
People preoccupied with their egos remain external to their prayers. The truly humble person feels small enough to "enter" even the tiniest word.