One may not tie a single knot on the drawstrings of a sweatshirt on Shabbat.

One should not tie the drawstrings of a garbage bag together in a bow knot as it is meant to last. A single slip knot is permitted. 

Knots that are prohibited to be made on Shabbat may not be untied on Shabbat. Therefore, one may not untie a permanent knot, such as a tzizit knot, on Shabbat.

One may untie an inadvertent knot that was formed while undoing shoelaces.

One may not undo the knot on a bakery box as it is considered permanent. It should be cut open instead.

Sanctity is achieved through immersion in Torah. Rav Pinchus Koritzer writes that the or haganuz (the hidden light) that Hashem concealed during creation, is hidden in the thirty six sections of the Shas. Learning Torah purifies our soul. In fact the Ramchal notes that if a rasha would learn Torah, he would repent, because the Torah awakens us, overtakes the evil inside of us, and brings us back to Hashem. The more effort we invest and the more desire we have to attain purity, the more Hashem will assist us. Rav Auerbach notes that there is a hint in the verse, "Lifnei mi atem mitaherim.... Before whom do you purify yourself and who will purify you...." Mi is the numerical equivalent of fifty. If we purify ourselves during the forty nine days of sefirah, Hashem will sanctity us on the fiftieth day, Shavuot.

After yetziat mitzrayim, the Jews had an awakening to sanctify themselves. Every year, Hashem sends down from above an abundance of purity.  We need only seize the opportunity. The Chafetz Chaim writes that when a Jew does a sin, the limb that performed the sin becomes impure. While some limbs are minor, damage done to the heart is critical and affects the whole body. Similarly, sinat chinam, which stems from the heart, draws impurity to one's entire being. Sefira is the time to rectify this and work on loving every Jew.

In Devarim the Torah writes, "No impurity should be seen in you or I will depart from you."  The Shechina leaves where there is immorality and immodesty. Conversely, it rests where there is kedusha. During sefira, a person must think about his moral conduct and dress and consider whether it is driving away the Shechina or bringing it closer.

Maintaining a level of kedusha entails drawing away from anything that is repulsive. This includes keeping one's person and surroundings clean so the Shechina can dwell among us. Our natural instinct is to recoil from anything repulsive. This is the response of the inner holy spark within each of us that cannot tolerate impurity.

Before performing a mitzva we say, "Asher kidishanu, Who has sanctified us," because all mitzvot purify us. There are 265 negative commandments and 348 positive commandments, which correspond to the limbs of our body. Every limb that performs a mitzva becomes a chariot for Hashem.

The Malbim says that a person can uplift himself above nature and connect to Hashem through bitachon. Trusting in Hashem causes Him to treat us in a supernatural way. Speaking in a refined manner purifies the heart. Our sages say, "Man is influenced by his actions." Speaking about the ideas of our holy sages brings kedusha into the hearts of those listening.

In Lecha Dodi, we sing, "Shabbat is the fountainhead of blessing." The more connected we are to Shabbat, the more sanctity we will imbibe. The Reishit Chochma writes that Shabbat is the source of holiness. We must draw from its kedusha for the rest of the week. The Chidah adds that when a person keeps Shabbat he attains such a holy level that drives away the impurity of his past sins.

May Hashem give us the ability to purify our hearts and souls in preparation for the great day of kabalat hatorah and may we merit to receive our true portion in Torah.

Question:

You once mentioned that childlessness is not considered yissurim shel ahavah (suffering out of love). If so, why do people suffer from it? In addition, if suffering comes from Hashem in order to help us get closer to Him, how can one person make another person suffer through ayin hara (an evil eye)?

Answer:

Hashem sends suffering upon a person not only out of love, but for the sake of tikun (rectification). According to the Arizal, most of us have already been on this world before and are here again to correct previous mistakes. Childlessness draws a person closer to Hashem, which is why all the avot and imahot were childless at the beginning, except for Leah. Therefore, it is fair to understand that childlessness is probably tikun. Tikun does not necessarily mean putting your finger on what is broken and fixing it. It means examining the options that are open to you and consistently choosing the best ones. In this way you will eventually reach your tikun, whether you know what it is or not.

Suffering comes from Hashem. However, he uses many different agents. There are many ways in which the same thing could happen. Suffering is sometimes meant to occur through human choice. For example, Hashem may place someone who needs to suffer near a person who has an ayin ra'a. This then would be part of Hashem's plan. An example of this was Sarah, who cast an ayin hara on Hagar. Even though Hagar brought about her own punishment through her actions, Hashem caused Sarah to cast an evil eye on her, so that her first child would be miscarried. This was the will of Hashem. True, there are many ways it could have happened, but it would have occurred anyway.  

Unlike a human who can only shoot one arrow at a time, Hashem can shoot many arrows at many targets at the same time. Every detail of a person's suffering, the way it happens, the duration of the suffering, and its effect on other people, are all a part of Hashem's perfect master plan.