The Gemara in Rosh Hashanah states that the transgression of not wearing Tefilin is in a special category of harshness. One who is not scrupulous to wear Tefilin is classified as "Karkafta D’la Manach Tefilin"-The scalp that does not don Tefilin and receives an extended sentence in Gehenom. Normally, the maximum sentence in Gehenom is twelve months. However, such a person stays in Gehenom until his soul is incinerated and his ashes are placed under the feet of the Saddikim.
The Rishonim debate what degree of not wearing Tefilin constitutes this special category of "Karkafta D’la Manach Tefilin." The Rif interprets the Gemara to mean someone who never wore Tefilin even once in his life. This seems to be Rambam’s opinion in Hilchot Teshuba. According to this opinion, if a person wore Tefilin even once, he is saved from being included in that category of sinners. The Rosh, however, questions the Rif’s interpretation, because the Rif’s text of the Gemara read "A scalp that NEVER wore Tefilin," whereas his text did not have the word "Never."
On the other hand, Rabbenu Tam understands the Gemara to refer to one who does not wear Tefilin because he is repulsed by them. However, if he doesn’t wear them because he feels that he is unworthy, he is not included in that category. For example he may be concerned that he cannot maintain a clean body or the proper intent. If that is his motivation, although he will be held accountable, he is not called a "Karkafta D’la Manach Tefilin."
If someone does not wear Tefilin, because he is lazy, The Bach holds that he is considered "Karkafta D’la Manach Tefilin." If it would be important to him, he wouldn’t be lazy, and therefore, it is considered a derision of Tefilin and included in Rabbenu Tam’s definition. Therefore, one must insure that his children and grandchildren don’t fall into this category and are diligent to put on Tefilin, even on vacation days, when sometimes them may be lax in this important Misva.
On the other hand, the Hida (Rav Haim Yosef David Azulai, 1724-1807) understood Rabbenu Tam to mean that only if one actively derides the Tefilin. Laziness is not included in that category. He brings a proof from one of Rabbenu Tam’s students, Rabbi Eliezer of Metz, who clearly states that one who doesn’t put on Tefilin because he is lazy, is punished, but is not considered "Karkafta…"
The Bet Yosef understands from the Tur, who did not make any distinctions, that the category of "Karkafta" applies to all circumstances.
This discussion underscores the supreme importance the Misva of Tefilin. While we are obligated to perform all the Misvot, there are certain Misvot that have more severe consequences than others.
Therefore, one must insure that his Tefilin are Kosher. If one’s Tefilin are invalid, he could put on Tefilin every day of his life and still, Has V’shalom, be considered "Karkafta D’la Manach Tefilin." To avoid this, he must buy the Tefilin from a reputable source and check them as mandated by the Halacha.
