In this pasuk the Navi implores us to do teshuvah. The Gemara teaches that this pasuk refers to the עֲשֶׂרֶת יְמֵי תְּשׁוּבָה the ten days from Rosh Hashana until Yom Kippur. Hashem is very close to us during this period. We can seek Him and call to Him, pleading for forgiveness, and thereby achieve atonement more easily.
Sefarim Hakdoshim expound on what an unfathomable gift teshuvah is. They urge us to be aware that the concept of teshuvah - that we can completely erase our earlier misdeeds, so that they are as if they never occurred - is a supernatural, special gift we have been granted.
Normally, a person's action can be forgiven but it cannot be undone. However, Hashem, in His infinite kindness has given us the special gift of teshuvah. We can make a firm resolution to abandon our old practices, fully regret our sins, confess, and make a decision to amend our ways, and amazingly that grants us a completely clean slate.
In the Vidui Hagadol of Rabbeinu Nisim, we say, "The way of Your righteous Beis Din is not like man's court"; In a human courtroom, a person who denies his crime, and pleads not guilty, can be acquitted and get away without punishment, even if he has committed an offense. Yet, in the Beis Din of Hashem, when one denies his misdeeds and does not confess, "Woe to him and woe to his soul". Hashem knows our aveiros, but if we acknowledge that we have stumbled, take responsibility for our errors, and abandon our old ways, Hashem has mercy on us.
Furthermore, we say in davening אַתָּה נוֹתֵן יָד לַפּוֹשִׁעִים - You extend a (helping) hand to sinners, to help them to do teshuvah. Not only does the Ribono Shel Olam accept our teshuvah, but He actually helps us do teshuvah!
Our teachers in their Sefarim cite many of the pesukim in Navi where we are encouraged to do teshuvah. They explain that all these nevuos were calls from our loving Father, through his messengers the Nevi'im, urging us to return to Him. Hashem is constantly showing us that there is a way to return. Even more so, once a year, during the Aseres Yemei Teshuvah, starting on Rosh Hashana, and culminating in the great, holy day of Yom Kippur, He gives us an even easier path back. During this time the path for teshuvah is completely open, and if we show a true desire to return, we will succeed.
Teshuvah is a great, supernatural gift that Hashem has granted us and He waits for us to utilize it and return to him all year, but the period of the Aseres Yemei Teshuvah is a time of exceptional closeness where Hashem reaches out and helps anyone that tries to repent. This is an amazing opportunity that we must not squander!