Lo With A Vav

The possuk (5:1) says אִם־ל֥וֹא יַגִּ֖יד וְנָשָׂ֥א עֲוֺנֽוֹ, the word לא  is written here with an additional ו. Why?  The midrash (6:5) sees this possuk not as a specific din regarding a witness that doesn't come forth to testify but as a general description of any averah.   In the words of the midrash: רַבִּי פִּנְחָס פָּתַר קְרָיָה בְּיִשְׂרָאֵל לִפְנֵי הַר סִינַי, וְנֶפֶשׁ כִּי תֶחֱטָא (דברים ט, טז): וָאֵרֶא וְהִנֵּה חֲטָאתֶם. וְשָׁמְעָה קוֹל אָלָה (דברים ה, כא): וְאֶת קוֹלוֹ שָׁמַעְנוּ מִתּוֹךְ הָאֵשׁ.  
Chassidus explains that when we have a קרי וכתיב the קרי reflects how things appear externally but the the כתיב is a reflection of what is happening in a deeper, hidden manner.  In the lingo the קרי is עלמא דאתכסיא and the כתיב is עלמא דאתגליא.
The idea of the קרי וכתיב in the context of  לא\לו is developed in the thought of the Sfas Emes in a few contexts.  Each time has its specific style and message but the gist can be summed up that by a feeling of לא, of nullification to Hashem, we are able to feel לו ,connected to Hashem.  A few examples are as follows.  In mizmor l'todah (100:3) it says וְל֣וֹ (כתיב וְלֹ֣א) אֲנַ֑חְנוּ עַ֜מּ֗וֹ וְצֹ֣אן מַרְעִיתֽוֹ.  The Sfas Emes Elul (5632) says ופי' הדבר הכל א' שכפי מה שלא אנחנו כן לו אנחנו.  Based upon one's feeling of לא, of self negation will equal how much a person is לו, connected to Hashem.  Again we find this expression in the Navi Yeshayeh (63:9) בְּכָל-צָרָתָם לא (לוֹ) צָר.  Says the Sfas Emes Vayigash, through the experience of לו צר, since we are helped by Hashem in the golus, therefore, לא צר we are able to not feel the pains of the golus.  In our parsha as well, says the Sfas Emes, ל֥וֹא יַגִּ֖יד is a person has the capability to drag his body (מגיד לשון המשכה) after his soul in order to bring out the greatness of Hashem in this world.  That is the additional ו, the ויו החיבור that one must be attach his body to the will of his soul.  The possuk isn't just a negative message but the words אִם־ל֥וֹא יַגִּ֖יד clue us in to the tikkun, if one is able to read it as לו יגיד to attach to Hashem then ונשא עונו will be in the sense of Hashem is נושא עון ועובר על פשע.