In addition to the above-mentioned points, a Synagogue ought to be distinguished by the greatest possible simplicity, by the absence of all kinds of images, portraits, or statues representing living beings, whether real or imaginary. The Jewish religion is void of every visible symbol; and the so-called magen-david (the double triangle) is probably not of Jewish origin, and has no connection with our holy religion. It is not a symbol of this kind, but some inscription of a passage from the Scriptures that in most houses of worship reminds us of the sacredness of the place. We enter it with due reverence, manifesting it outwardly, in our peculiar traditional manner, by keeping the head covered. It is our ancient custom to cover the head when engaged in prayers, in reading the Bible or Talmud and their commentaries. This outward sign serves to remind us that not only our Service but even our literature is something holy, and its study a religious act (‏מצוה‎). [148] Before we proceed to describe the details of our ritual, we mention one important point in which the present Synagogal Service differs from the ancient Service in the Temple. From what we are told in the Scriptures and in the Talmud, we learn that instrumental music was an essential element in the Service, and that King David and his successors paid great attention to it, whilst, with a few exceptions, it is almost entirely absent from our Synagogues. The principal reason why instrumental music is excluded from the Synagogue is its prohibition on Sabbaths and Holy-days by Rabbinical law (Babyl. T., Erubin 104a). This prohibition, like many other enactments, did not apply to the Temple Service; for the sacrificial laws had to be obeyed, irrespective of the fact that they involved acts which, if performed apart from the Temple Service, would constitute a breach of the Sabbath laws. Apart from the Temple Service the Sabbath laws remained in full force for the priests as well as for the general public.