What does that mean? If you want to develop a personal relationship with HaShem, you need to do teshuvah every single day. If you don't set time aside, and really review your day and confess and regret each and every cheit, (sin) you won't be able to experience HaShem. Instead, all your transgressions will cloud your spiritual awareness of HaShem and you will essentially be living in the spiritual dark-ages.
While I was giving a dvar Torah on Shabbath, (Shoftim) I mentioned Elul, and how the King is in the Field. In Elul, HaShem makes Himself accessible to everyone. The rest of the year, we need to approach the palace, enter rooms within rooms and plead and beg to receive an audience with the King. But, in Elul, the King is in the field. Right there with us, the peasants.
The juxtaposition of the two ideas made me realize a deeper message: The nature of 'the King is in the field' is a result of the deep teshuvah that is happening in Elul. Access to the King is directly proportional to teshuvah. We can have the close relationship with HaShem of Elul year round if we do the avodah of Elul, teshuvah, year round.
I believe I read a long time ago that Elul embodies the passuk השיבנו ה' אליך ונשובה, (return us to you, HaShem, and we will return) and the rest of the year embodies the passuk, שובה אלי ואשובה אליכם. (return to me [Israel] and I will return to you) When I mentioned this relationship to Rav Raz Hartman he clarified it for me. Elul is when HaShem does Teshuvah and comes close to us. The rest of the year we do Teshuvah to come close to HaShem.
The important thing to realize is that, as Rebbe Nachman teaches, Teshuvah is the fundamental building block of any relationship with HaShem. Elul is special because of the special ease with which teshuvah can be done in Elul.
If we stop to think about it, it's obvious, what does Teshuvah mean? Returning. Coming back to HaShem. Closing the gap.