I received a pair of tefillin from my grandfather (of blessed memory) when I became a bar mitzvah about ten years ago, and now I’ve started wearing them regularly. Since he was a religious man, do I have to check that they’re kosher, or can I rely on the fact that he was Jewishly knowledgeable and assume that they’re OK?
Tefillin definitely have to be “kosher”. The laws governing the making of the boxes and the parchments of tefillin are very complicated and involved, as well as the laws of actually writing the relevant passages on the parchments. This means that they absolutely must be obtained from G-d fearing, reliable tefillin- makers and scribes.
There are certain requirements that can’t even be detected after the writing of the parchments and the construction of the boxes are complete. And even if all was prepared correctly, tefillin that were not properly kept could become damaged and rendered unfit.
In cases such as yours, even well-meaning and observant grandparents (or other such family members) are often not knowledgeable enough or careful enough to buy good-quality, kosher tefillin from properly reliable sources. Also, the matter of years of disuse calls in to question whether the tefillin were properly guarded from possible damage.
Therefore you certainly must have the tefillin checked by a G-d-fearing expert to make sure that you are, in fact, fulfilling the mitzvah of tefillin as you intend. If, for whatever reason, they are found to be unkosher and cannot be repaired, while they may have sentimental value to you, that’s not enough to be able to use them for the mitzvah.
In such case, regarding having already used them, even though technically you may not have fulfilled the mitzvah, be assured that G-d is certainly pleased with your good intention, in which your departed grandfather has a part and from which he derives spiritual benefit, but you’ll still have to acquire (either by buying or borrowing) a kosher pair.
When Rabbi Israel of Rozhin passed away, his sons decided to distribute his belongings among themselves according to lots. It turned out that one of his younger sons received the prized tefillin of their grandfather, the great Maggid of Mezritch. When two students of the eldest son heard that he was upset over not having received the tefillin, they secretly removed the parchments of the Maggid’s tefillin and replaced them with other kosher ones, it being their intention to give the illustrious parchments to their rabbi at a later opportunity.
After two years, that opportunity arose. But when the eldest brother found out what they had done, he was beside himself with grief at the thought that his younger brother had used kosher, but fake “Maggid-tefillin”, for all that time. He rushed to his brother’s town only to find that he had two pair of tefillin, one which he wore, and another, the Maggid’s, which he would take in his hands, gaze at, and with a sigh, return to their place.
When his older brother asked him the reason for this odd behavior, the younger replied that since having received the tefillin, he somehow, unexplainably, felt it improper to use them but rather longed for the day that he would feel fit to wear them. Realizing that it was precisely his younger brother’s righteousness which guarded him from using the imposter pair, the elder brother told him the true story and explained that it was not he who was unfit for the tefillin, but rather the tefillin were unfit for him.