It says in Parashath Terumah, "We'Asu Aron 'Aseh Shittim, "And you shall make an Ark of acacia wood". It says in 'Od Yoseph Hai, just as the Aron was the place where the Luhoth Habberith (the Tablets of Stone, [which were the Ten Commandments and effectively included the entire Torah]), were kept and protected, so too, a person's heart is the place where the Torah is kept and protected in a person.
When the Torah is in our heart it is protected, meaning no one can come and steal it from us. However, we have the abilty to lose it ourselves. How is that? This is done by not reviewing the Torah and relying on the fact that there are Sefarim (books), or perhaps computers, where we can look up what we need to know. The problem with this being that if we are unable to find it in the books, then that Torah is lost to us.
So the only protection that we have to ensure that the Torah is, in fact, kept and protected in our heart, is to constantly learn and review the Torah.
(See 'Od Yoseph HaiDerashoth, Parashath Terumah)
