In Parshat שופטים there is a discussion regarding the testimony of witnesses. The Torah says, על פי שני עדים או שלושה עדים יקום דבר, by the mouth of two or three witnesses, shall a matter be established.
The question raised by the Rabbis is what is learned from the words, על פי, by the mouth of. There is a מחלוקת ראשונים on the matter.
According to Rabbeinu Tam in Tosfot, the על פי is coming to exclude the testimony of an אילם, one who cannot speak. As long as the witness is capable of speaking, he is also able to testify in writing.
The Rambam disagrees and says that according to the Torah, both cases of ממונות and נפשות, money matters and capital cases, must be done by way of oral testimony. The Rabbis made a leniency to allow written testimony in money matters, so that lenders will have an easier time getting paid back.
It’s important to recognize that every word of the Torah needs to be examined for its special meaning and significance.