The Ramban (Vayikra 13, 47) writes that tzora'as is a completely supernatural phenomenon. It occurred only in the chosen land of Eretz Yisroel, it befell only the Jewish People, and only when they maintained an elevated level of spirituality. When an aveirah was committed in such a spiritually charged environment, Hashem caused tzora'as to appear on the sinner's house, clothing or body to indicate that He had distanced Himself from the offender as a result of the transgression. Unfortunately, due to the yeridas hadoros (diminishing of the generations), we no longer experience this extraordinary form of communication from Hashem.
Rav Wolbe (Olam HaYedidus pg. 107) notes that the "world" claims the exact opposite: In truth there is an aliyas hadoros, since each generation advances with great strides in comparison to previous generations. They point to the advances made in science, medicine, technology, agriculture and almost every other aspect of the physical world. If so, asks Rav Wolbe, wherein lies the yeridas hadoros; in what respect are the generations following a path of continuous descent?
Rav Wolbe cites a Gemara in Sanhedrin (106b) that deals with this question almost precisely. "Rava said: in the era of Rav Yehuda Torah study was limited to the order of Nezikin (monetary damages) while we study the entire Shas. . . However, [when there was a famine and] Rav Yehuda would remove one of his shoes (an act demonstrating self imposed suffering) rain would fall, while we cry out [for rain] and no One pays attention. [Despite that from the quantity of Torah studied we seem to be on a greater level, nevertheless] Hashem desires the heart, as it is written "And Hashem sees the heart." The decrease in generations relates to the heart.
What exactly is this "heart" that we are missing? It can be understood as follows: Our minds process information with logic such as cause and effect. In contrast, our hearts have a more direct understanding because they perceive things more clearly, as the pasuk (Koheles 1, 16) states, "And my heart has seen much wisdom." For example, when we speak about someone, we describe his appearance, portray his personality, relate his history and define his significance. This entire character assessment is a product of our minds. In contrast, when I speak to someone and thereby become impressed by his qualities, intelligence and behavior which in turn causes feelings of love or sympathy, these feelings are an outgrowth of our hearts. The heart perceives someone or something standing before it, and the encounter leaves an indelible impression upon the heart.
When Chazal tell us, "Hashem desires the heart" it means that intellectual comprehension is not enough. The knowledge must penetrate our hearts. True understanding and belief is only achieved when the heart understands and believes. As Rashi writes (Shemos 20, 19) "There is a difference between what a person himself perceives and what others relate to him, because when others relate things, sometimes his heart fails to believe it."
This idea applies with regard to both mitzvos bein adom la'Makom and mitzvos bein adom la'chaveiro. We are commanded to, "Love Hashem with all your heart." Torah should be studied in a way that we see the topic being discussed as a reality before our very eyes. The knowledge gained cannot remain as a mere intellectual acquisition, but must penetrate our hearts in a way that affects our way of life. Additionally, we must relate to others with a true, heartfelt understanding. Many times we are aware of another's difficulties but fail to let this knowledge penetrate our hearts in a way that will allow us to make a difference in their lives. Chazal tell us (Eiruvin 53a), "Rav Yochanan said, the hearts of the earlier generations were wide like the opening of the Ulam (twenty cubits), and the hearts of the later generations were wide like the opening of the Heichel (ten cubits), and our hearts are as wide as the opening of a needle."
The above relates to the size of the hearts after their avodah. Without avodas Hashem there is no "heart" at all. Chazal tell us, "What is the avodah of the heart? Tefillah." When one davens he is supposed to picture himself standing before Hashem. When the heart perceives Someone opposite it, it makes an indelible impression. Using the avodah of tefillah is one of the ways we can develop our hearts.
Despite the yeridas hadoros, the commandment to love Hashem, and the obligation to perform His mitzvos with our hearts, remains binding. The past few hundred years have brought novel approaches to aid people in becoming more in touch with their hearts. The Baal Shem Tov introduced Chassidus and Rav Yisroel Salanter introduced a new manner of mussar study. Whatever path we choose, if it brings us to serve Hashem with more of a heart, then we will have achieved significant success because, "Hashem desires the heart."