There are no stories in the Torah for story's sake. So if the Torah tells us ויקם מלך חדש אשר לא ידע את יוסף, the Torah is teaching us a lesson. The meforshim explain that each Yid has his own personal obligation to go from מצרים. That is we each have little of מצרים within us. Yosef essentially sustained מצרים and saved מצרים from oblivion, yet in this week's parsha we find that ויקם מלך חדש על מצרים - whether he was literally new or he made himself out as new, it is inconceivable that he didn't know Yosef. Instead, he made himself out "as if" he didn't know him. The RBSO sustains us too and saves us from oblivion. Yet, we (certainly I) make ourselves like פרעה, "as if" we don't know Hashem. Intellectually we know we are reliant on Him, but we conduct ourselves "as if" He doesn't exist. Like פרעה, we think הבה התחכמה לו we can outsmart מושיען של ישראל, that is we build ערי מסכנות security nets for ourselves, thinking that we don't have to be reliant on the RBSO.
The Torah teaches us that these ערי מסכנות are not ראויות מתחלה לכך - they are not meant as a substitute for the reliance we need to place on Hashem. And, if we don't learn this lesson, the RBSO says, "I will bring you to a situation where you will bring about your own downfall. You will nurture the one who will bring the מכות upon yourself. And ultimately, even פרעה will come to say: 'חטאתי הפעם ה׳ הצדיק ואני ועמי הרשעים'."
May we be Zoche to recognize the easy way how to truly "know" the מלך העולם.