Invisible Walls

We say in the מזמור לתודה (Tehillim 100:3) הוא עשנו ולא [ולו] אנחנו.  What is the connection between the קרי וכתיב, the writing of the word לא, no to the way it is pronounced, לו, we are to Him?  The Sfas Emes in a few places in his maamereim on Elul (for ex. Shoftim 5768, Ellul 5762, littutim letter from 5625) cites the Chidushay HaRim says that how do we become close to Hashem, ולו אנחנו, through ולא אנחנו, nullifying ourselves to Hashem.  The spelling of the word is the key behind the pronounced word.  

The same type of קרי וכתיב appears in out parsha (25:30) regarding one who sells a house in a walled city and does not redeem it back within a year, it belongs to the new owner forever.  ואם לא יגאל עד מלאת לו שנה תמימה וקם הבית אשר בעיר אשר לא [לו] חמה לצמיתת לקנה אתו לדרתיו.  The כתיב is לא, it does not have a wall but the קרי is לו , it does have a wall.  Why would the Torah write a word that indicates the complete opposite meaning ,that it doesn't wall a wall, when it means to say it does have a wall?  

When a person buys and sells property, it gives them a sense of ownership over that which they have acquired.  There is a feeling that the person's acquisition gives him control over the property.  Then yoval comes and demonstrates that is not the case, a person's acquisition's do not last forever.  What a person builds will be toppled by the passage of time.  However, there are those that build walls around their properties.  They fortify themselves against the forces that which to topple their accomplishments and feel that way they will outsmart the winds that seek to take over.  However, eventually even the walled structures ,the great societies of history get conquered and washed away through the passage of time.  what is the only wall that lasts?  The לא חומה, the invisible wall of Torah (see Pesachim 78a חומה זו תורה.)  It is the Torah wall, the walled cities מימי יהושע בן נון, that ensure last eternally (this paragraph is based upon an article by Rabbi Y.Y. Jacobson.)  Again the כתיב tells us the key to understanding the underlying principle (in the ruchniout aspect,) of the possuk.