The Tochachah and the Concealed Good
Immense growth comes from the times when it is hard to serve Hashem, and we add that immense growth also comes from the hardships of life.
The Gemara (Menachos 29:) states, רבי עתיד הלכות של תילים תילי וקוץ קוץ כל על לדרוש עקיבא, "Reb Akiva will teach many halachos from each edge of the letters." The Or LaShamayim zt'l (Lech Lecha 'ה ויאמר ה"ד) explains that from every קוץ, thorn, and hardship, Reb Akiva grew, and because of them he became an expert in Torah. Each challenge in life elevates a person immensely.
The Chofetz Chaim zt'l compared the tests and hardships of life to gold miners. These people pan through dirt and mud, break through heavy rocks, and become covered in black and mud, but they are extremely happy because gold is so valuable. They don't care if people laugh at them because they know that they are earning large amounts of wealth.
The same can be said about people who experience difficult tests and challenges in life. They appear black; they work hard but aren't upset because they know they are earning so much.
The Black of the Eye: Seeing Through Darkness
The Midrash (Bamidbar Rabba 15:7) states, "You have eyes that are white and black, and you only see through the black. Hakadosh Baruch Hu is entirely light; does He need your light? [So why is there a mitzvah to light the menorah?]"
The Orchos Chaim (see also Sifsei Tzaddik, Behaaloscha) explains the Midrash by saying that a person goes through various moments in life. Sometimes, he goes through good times, which is represented by the white of the eye. And sometimes, he struggles through difficult times and feels that the world has turned black for him. These times are represented by the black of the eye. Many people mistakenly think that the best times of their lives are when Hashem's light and kindness shine on them. Therefore, the Midrash tells us, "You only see through the black..." It is from the difficult, challenging times of life that you merit to see Hashem and to reach high levels.
In the parshiyos of the tefillin it states (Shemos 13:16) ידכה על לאות והיה. Chazal say that ידכה stands for כהה יד, the weaker arm (and that is the left arm). A person has two eyes, two ears, two nostrils, and they are both just as strong. But the arms, Hashem created differently, where a person does most of his work with his right arm, since the left arm is weaker. The straps of tefillin need to be completely black (מסיני למשה הלכה). Tefillin is a sign of the connection between Bnei Yisrael and their Father in Heaven. When it appears dark, we merit a close connection with the Creator. The mitzvah of tefillin is to wear them specifically on the left hand, the weaker hand, to show that during periods of weakness, times of tests, and moments of darkness, one can attain deveikus to Hashem yisbarach.
