Shoftim - Inside and Outside

And it will be, when he sits upon his royal throne, that he shall write for himself copies of the Torah on a scroll from [that Torah which is] before the Levitic kohanim.

וְהָיָה כְשִׁבְתּוֹ עַל כִּסֵּא מַמְלַכְתּוֹ וְכָתַב לוֹ אֶת מִשְׁנֵה הַתּוֹרָה הַזֹּאת עַל סֵפֶר מִלִּפְנֵי הַכֹּהֲנִים הַלְוִיִּם

Devarim 17: 18

What are these copies of the Torah?

Rashi explains the verse as:

Heb. מִשְׁנֵה הַתּוֹרָה i.e., two Torah scrolls, one that is placed in his treasury, and the other that comes and goes with him (San. 21b). [I.e., a small scroll, which the king carries with him. Thus the Talmud derives מִשְׁנֵה from שְׁנַיִם, two.] Onkelos, however, renders פַּתְשֶׁגֶן, copy. He interprets [the word] מִשְׁנֵה in the sense of repeating and uttering. [I.e., one copy of the Torah, which the scribe would write while uttering the words before he writes them, deriving מִשְׁנֵה from שִׁנּוּן, studying .]

First Torah Scroll: Behavior in Private
The Slonimer Rebbe in Netivot Shalom explains the significance of the two Torah scrolls. He says that the Torah scroll that is placed into the treasury (the hidden Torah) is reminiscent of the opening to Shulchan Orach Orach Chaim, where it says:

For the way in which a person sits, moves around, and carries out his daily activities while he is alone his house is not the same way he should engage in these activities while standing before a great King. 

That just as this Torah scroll is stored away, so also when you are alone, by yourself, in your home, you should place Hashem before you always. This can serve to influence your behavior and keep you from being at risk to sin.

Second Torah Scroll: Affecting Your Daily Life

The Rebbe continues and explains that the other Torah scroll, which comes and goes, should serve to remind you of Hashem's presence in all your mundane activities.

As the Rambam elucidates:

A person should direct his heart and the totality of his behavior to one goal, becoming aware of Hashem, blessed be He. The [way] he rests, rises, and speaks should all be directed to this end. 

For example: when involved in business dealings or while working for a wage, he should not think solely of gathering money. Rather, he should do these things, so that he will be able to obtain that which the body needs - food, drink, a home and a wife.

Similarly, when he eats, drinks and engages in intimate relations, he should not intend to do these things solely for pleasure to the point where he will eat and drink only that which is sweet to the palate and engage in intercourse for pleasure. Rather, he should take care to eat and drink only in order to be healthy in body and limb.

The second sefer Torah should seemingly accompany you in every thing you do, and influence your decisions. This is meant to keep you straight and honest.

 We should all merit to feel the awareness of Hashem both in private and in our public interactions.