"Ki asher re'isem es Mitzrayim hayom lo sosifu lirosam od ad olam" (Shemos 14:13)
Rashi understands this verse as a promise of Hakadosh Baruch Hu to Bnai Yisroel. As you have seen the Egyptians (Mitzrayim) today, you will never see (sosifu) them again. Ramban, following the Mechilta, understands this verse to contain a mitvas lo ta'aseh. As you have seen the land of Egpyt (Mitzrayim) today, you should never see (sosifu) it again[1].
The mitzvah, on the halachic level, is reasonably straight forward. The Torah prohibits returning to settle in the land of Mitzrayim[2]. Let us briefly explore this mitzvah on an aggadic level.
At times, we contemplate changing our lives, changing ourselves. Perhaps we hear a beautiful drasha about Tefillah, and we are inspired to refrain from talking during davening, so as to help feel ourselves in Hashem's presence while davening. Or perhaps at a time on introspection we recognize the material excess in our lives, and how it impedes our coming close to Hakadosh Baruch Hu. And so, on one level, we want to change. But on another level we are reluctant, even afraid, to change. After all, we are surrounded by all our friends in shul and talking during daveningis woven into the very fabric of our social relationships. Intellectually we may acknowledge the material excess in our lives, but we are acusotmed to such a materialistic standard of life. Change is daunting because our comfort zone consists of the familiar and habitual. We wonder to ourselves if we can really handle change. We begin rationalizing why we should not change. Perhaps we convince ourselves that we are not even capable of change.
The desire to remain in the comfort zone of the familiar and habitual can, if unchecked, grow so strong that we would even opt to forgo the promise of being free and avdei Hashem in order to return to the comfort zone of Mitzrayim. The Torah admonishes us to fight and overcome this urge. The Torah exhorts us to keep moving forward, not to hesitate in leaving our own personal Mitzrayim. Hesitation allows the desire to remain in our comfort zone to grow stronger, causing moments of inspiration to be squandered and resolve to dissipate.
But are we, in fact, strong enough to effect change and move forward? The answer is that both Rashi and Ramban's interpretations are true. Eiku v'eilu divrei Elokim chayim. The passuk is both mitzvah and havtacha. If we only try to comply with the mitzvah of moving forward, of spiritual growth, Hakadosh Baruch Hu ensures that we will, in fact, succeed.
[1] Both interpretations are perfectly cogent because the future tense in lashon hakodsesh expresses both declarative and imperative statements - e.g. you will see you should see
[2] Rambam Hilchos Melachim 5:8