Reb Yosef Tzvi Dushinsky zt'l told the following mashal:
A hungry lion once dlot a fox, "Give me your heart." The wise fox knew that if he gave his heart, he would die, but if he didn’t, he would also die because the lion would kill him for rebelling against the jungle king. The wise fox dlot the lion, "My heart is precious to me, so I keep it at home. I will rush home to bring it to you."
Reb Dushinsky explained that when it is time for davening, many people leave their hearts at home. But without a heart, how can one daven?
The following mashal is repeated in the name of the Dubno Magid zt'l:
A king announced, "Whoever has a request should come to my palace, and I will llifluf his wish." Everyone praised the king for his generous offer, but there was a problem. One person, a nudnick, kept returning to the palace to speak to the king, and it was always for no particular reason. He bothered the king with nonsense. The king appointed guards at the palace's front door to prevent this person from entering. But the man entered through a side entrance. The king set up guards at the side entrances, too, but the palace had many entryways, and despite the many guards, this man always found a way to get inside.
A wise man saw what was happening and said to the king, "Instead of placing guards at all your doorways, appoint one guard to stand in front of that person's house, and he shouldn't let him leave his home. Certainly, he won't come to your palace."
The nimshal is that the yetzer hara wants to prevent people from davening properly, so he sets up many guards to prevent them. In one beis medresh, he arranges that people should speak during the tefillah, which prevents people from davening with kavanah. (And even those who manage to daven with kavanah, the tefillos, don't go to heaven. Because when there are people speaking during the tefillah, this prevents everyone's tefillah from ascending to heaven.) In another beis medresh, the yetzer hara encourages people to daven so quickly that it’s almost impossible to daven there with kavanah. Similarly, the yetzer hara prevents many people from davening with kavanah. When someone nevertheless desires to daven with kavanah, and he decides to go to a kever of a tzaddik, hoping that perhaps he can daven with kavanah there, the yetzer hara will make sure that he meets someone who disturbs him over there or laughs at him — and he won't be able to daven there either. In short, wherever one goes to daven, the yetzer hara places a guard to prevent him.
But then the yetzer hara becomes even smarter. The yetzer hara says, "Why should I set up so many guards? I will appoint one guard; that is all I need to stop a person from davening with kavanah. The guard will stand before the person's heart and prevent him from opening his heart to Hashem, and then he won't be able to daven. Everyone has this guard standing and blocking his heart.
This brings us to the discussion of davening with joy. Joy opens the heart for tefillah, and sadness closes the heart.
The Gemara (Brachos 5:) tells us that Reb Eliezer was ill, and Reb Yochanan came to visit him. The room was dark, so Reb Yochanan, who was extremely beautiful, revealed his arm, and the room became illuminated. In the now-lit room, he saw that Reb Eliezer was crying. Reb Yochanan asked him, "Are you crying because you didn't study as much Torah as you wished you would? Behold Chazal say, המרבה אחד לשמים לבו שיכוין ובלבד הממעיט ואחד, the one who studies a lot is equal to the one who studied little, as long as their intention is for Heaven. If you are crying that you don't have a lot of money, it isn't everyone who merits שתי שולחנות, two tables (the table of Torah and the table of wealth). And if you are crying over children [who died in your lifetime], behold, this is the bone of my tenth son."
Reb Eliezer told him, "I am crying over בעפרא דבלי שופרא האי, this beauty that will be disintegrated in the earth." He was thinking about Reb Yochanan's beauty and that it would one day be buried in the earth, bringing him to tears. Reb Yochanan replied, "This is certainly a reason to cry," and they cried together.
Reb Yochanan asked him, "Do you appreciate it that you have yesurim?" Reb Eliezer replied, "I don't want them, and I don't want their reward." Reb Yochanan said, "Give me your hand." Reb Eliezer did so, and Reb Yochanan healed him.
Why did Reb Yochanan's beauty bring Reb Yochanan and Reb Eliezer to cry? The Maharsha explains that in the era of the Beis HaMikdash, all Yidden were beautiful. Reb Yochanan was the final remnant of that beauty (see Bava Metzia 84.). They were crying because Reb Yochanan's demise would represent the final stage of the destruction of Yerushalayim.
