[Moses told the Levites,] "Take this Torah scroll and place it alongside [the Tablets of Testimony]."
Thus, the Ark in the Tabernacle contained the Torah both engraved in stone and written on parchment. The difference between engraved and written letters is that the engraved letters are part of the parcel of the stone, whereas written letters are not part of the parchment but added to it. Thus, engraved letters express our intrinsic connection to the Torah, whereas written letters allude to how we preserve our connection to the Torah even during our mundane lives, when we think of ourselves as being separate from the Torah.
The presence of both the engraved Torah and the inscribed Torah within the Ark indicates that we must first experience our intrinsic connection with the Torah and then carry that experience with us into our mundane lives.