The Maor Vashemesh (Yisro, פסוק על עוד ה"ד) writes, "When a person turns thirteen and he begins to wear tefillin, he receives from heaven divine perception and a great holiness. If he guards this kedushah, the kedushah will remain with him, and he will grow higher every day. The wise should be cautious to grab, with both hands, all the treasures that are given to them. One shouldn't be a fool who loses everything he receives. The Sefer HaPardes has already written, "There is a kabbalah that when a child turns thirteen, and on that night, makes up his mind to serve Hashem, ויעלה יצמח, he will grow and rise to high levels."
The Rebbe pointed to the light fixture hanging from the ceiling and said, "The light switch is on the wall. How does the chandelier turn on? The answer is that wires connect the chandelier to the light switch. Similarly, the straps of the tefillin bring down the holiness of the tefillin into the person."
Some tzaddikim would bond the tefillin on the arm of a bar mitzvah bachur with a lot of force. This was to hint to the bachur that he should be bound to the kedushah of the mitzvah with a tight bond.
My grandfather, Rebbe Moshe Mordechai zt'l, said that his grandfather, Rebbe Dovid Biderman zt'l put tefillin on his arm so tightly that he thought his arm would fall off. He repeated this in his old age and said, "I still feel that time I wore tefillin."
We aren't on that level, but we should strive that when we put on tefillin, the effect should remain with us throughout the day. We should feel the kedushah of the mitzvah in our neshamah.
When one turns thirteen, Hakadosh Baruch Hu gives him a present: the holy malach called טוב יצר, who will always be at his side to help him serve Hashem and overcome the yetzer hara.
Reb Shimon of Yaroslav zt'l explains the pasuk (Tehillim 119:9) כדברך לשמור ארחו את נער יזכה במה. This means, why does a נער, a bar mitzvah bachur, receive ארחו, his guest, the yetzer tov? The answer is כדברך לשמור, so he will be able to keep the mitzvos.
Rebbe Moshe Mordechai of Lelov zt'l said to a bar mitzvah bachur, "It is the way of the world to honor a guest with food and drink. The host gives the guest the refreshments that the guest enjoys. A bar mitzvah bachur also receives a guest. The guest is the yetzer tov. The yetzer tov enjoys a blatt Gemara. Therefore, honor your guest with a lot of Gemara."
Reb Moshe Mordechai would also often repeat the following vort written by the Or Lashamayim of Apta (Netzavim). It states (Bereishis 10:10) וארך בבל ממלכתו ראשית ותהי, which means, the first acceptance of malchus Shamayim is בבל, to learn Talmud Bavli. If he does so, וארך, he will have arichus yamim and health. (One of the translations of ארך is health.)
This chapter of Tehillim (2) discusses tefillah, as it states ואתנה ממני שאל, "Ask from Me, and I will give..." This hints at the great power of tefillah that a bar mitzvah bachur has on the day of his bar mitzvah, particularly when he davens for ruchniyos. שלם בלבב ולעבדו רצונו ולעשות ,ויראתו אהבתו בלבנו וישם ,בתורתו לבנו יפתח הוא, "He shall open our hearts in His Torah, and place in our hearts fear and love of Him, to do His will and to serve him with a complete heart."
The Zohar (vol.2, 98.) states, "Whoever turns thirteen, he is called ישראל לכנסת בן, a son to Knesses Yisrael. This is because before this age, he isn't a בן, and the Shechinah doesn't reside on him... [At thirteen, Hashem says] (Tehillim 2:7) ילדתיך היום אני, I gave birth to you today. Because before this age, he wasn't called בן, and he didn't have the divine soul. But ילדתיך היום, this day [when he turns thirteen] ילדתך, I gave birth to him, and not the sitra achara."
