The Medrash (39,1) introduces Avraham with the following mashal
ויאמר ה' אל אברם לך לך מארצך וגו' ר' יצחק פתח (תהלים מה) שמעי בת וראי והטי אזנך ושכחי עמך ובית אביך אמר רבי יצחק משל לאחד שהיה עובר ממקום למקום וראה בירה אחת דולקת אמר תאמר שהבירה זו בלא מנהיג הציץ עליו בעל הבירה אמר לו אני הוא בעל הבירה כך לפי שהיה אבינו אברהם אומר תאמר שהעולם הזה בלא מנהיג הציץ עליו הקב"ה ואמר לו אני הוא בעל העולם.
Avraham's search for Hashem in the world is analogous to a person (Avraham) who was passing from one place to another and came upon a sight of a palace which was in flames. He asked himself can this be possibly true that there is no owner to the palace which can stop its burning? Immediately after his astonishment, the owner of the palace (Hashem) peeked out from his hiding and declared I am the Baal Habayis of this palace and I am asking from you לך לך.
Why is the world, in Avraham's journey to discover Hashem described as a burning castle and not just a plain castle? Secondly, why was a castle chosen to be the object of his realization that proved that the creation is not a product of happenstance but rather a designed product of a power originating from an extra ordinary force beyond human intelligence and capability. Any phenomenon of nature would warrant and back the same absolute conclusion that some super power outside of the universe willed and created it all from nothing?
The Sefer Pardes answers these two questions as follows. Avraham excelled in the middah of chesed תתן אמת ליעקב חסד לאברהם . He arrived and toiled to perfection this middah because when he looked at the world he saw Hashem's chesed in every particle of creation as the passuk says (Tehillim 89,3) עולם חסד יבנה . Avraham's name is even hinted in the Hashem's act of creating the world as the passuk say אלה תולדות השמים והארץ בהבראם which share the same letters as באברהם with the middah of Avraham which is chesed. When Avraham realized Hashem's incredible act of kindness to create such a world to benfit mankind, his deep passionate love for Hashem naturally drove him to fulfill the commandment of והלכת בדרכיו to emulate Hashem's middah of chesed and he taught others to do the same ויקרא בשם ה'.
This is why the Chazal used the word בירה a castle to describe the world in Avraham's perception. A castle is not merely a place to find protection from outside elements and dangers. It is a place where one can enjoy himself immensely with all sorts of royal benefits and ambience; of lavish food, fancy furniture, servants, finery, a beautiful garden to relax in, music etc. This בירה is a mashal to the בריאה that Hashem created for man. The Medrash writes that when Adam was created Hashem took him personally on a tour to show to him how beautiful creation is and how there are so many different kinds of foods, vegetation, animals etc all for him to enjoy. How wonderful it is that Hashem created and displayed so many colors in everything. The world would have functioned fine with everything being formed with just two colors black and white But no Hashem wanted Adam to enjoy this world and recognize Hashem's display of ultra and utmost chesed to his creation. At the end of the tour Chazal say that Hashem told Adam As beautiful and balanced that the world is which I created for your benefit , please make sure you don't ruin it.
כיון שברא הקב"ה את אדם הראשון נטלו והוליכו באילני גן עדן וא"ל ראה את כל מעשה אלהים מה נאים לך מה משובחים לך, כל מה שבראתי בשבילך בראתי, אל תקלקל מעשיך
However, as Avraham gave a closer observation of the population living in this wonderful castle he began to realize that this castle possesses a negative side to it as well called fire. He understood that if one constantly indulges in the pleasures of the earth he himself will become earthly and burn the neshmah that also dwells within him. If man is drawn to the sheker and darkness he will lose control over the reins to his bodily cravings, and the earthliness that he indulges in will make him self destruct and transform into a mere clod of earth without neshama. If he gravitates to spirituality and emes then he will take from this world materialism for the purpose of furthering an intimate relationship with his creator and elevate the world to a higher level. This is hinted to Hashem's closing words to Adam אל תקלקל מעשיך whose acronym is אמת the same acronym that is alluded to in the end letters of the first three words of the Torah .בראשית כרא אלקים
Avraham realized that the world is composed of a paradox, one that it gives pleasure and one that through this pleasure it will bring destruction. Avraham therefore asked מי בעל הבירה who is the owner creator of the world in order to receive from Him instructions how to safely journey and navigate successfully through this life of a בירה דולקת .
It was then that Hashem revealed himself to Avraham and said לך לך מארצך . This בירה is not the final destination. There is another world called Olam Habah where the ultimate of chesed through giving reward will take place. This world is only a means and corridor to get entrance to the next world. Therefore I am instructing you לך לך מארצך leave yourself and your desire for earthliness. Cling to me and my wishes and you will find both happiness and contentment in this world and even more so in the next.
Hashem gives us the present of Shabbos in order to strengthen us to ensure that our spiritual GPS is functioning properly. Shabbos which is 1/60 מעין עולם הבא reminds us that this world is fleeting, temporal, and serves only as a corridor to the Next World. Don't let your work become your quicksand where one slowy sinks into earthliness and cannot climb out. לך לך go to you. Who are you really? You are essentially core neshama not body. You are created with a neshama in order to get eternal spiritual reward in Olam Haba. The letters of לך are also כל which Chazal say that "everything" refers to Olam Habah for this world of the Fiery Castle is only for the purpose of attaining Olam Habah (Baba Basrah 17b top). Hashem is telling Avraham that this is the real you the neshama which will soon reside in Olam Habah with pleasures beyond anything in this world.
On Shabbos a Yid is aided in placing the letter א which represents Hashem אלופו של עולם in the בירה to make the word בריאה a healthy creation. The word בריא means healthy and the letter ה symbolizes this world (Menachos 29b). If one indulges in too much physicality he will have a fallout from the ה by burning his neshama and warranting a tikkun in the fire of Gehenum. If the spirit of Shabbos is preserved correctly then the gematria of בריאה דולקת equals .יום שבת On Shabbos we are ingnited with a heavenly fire that does not consume like we found in the episode (Shmos 3,2) הסנה בוער באש the thorn bush is burning but it is not consumed. The gematriah of הסנה בוער באש עה"כ equals שבת. On Shabbos through Hashem's gift to us with the neshama yesairah we become infused with emes and not the sheker of the castle.
This can be seen from the ending letters of Parshas Vayechulu which we say on Shabbos ברא אלקים לעשות which spell אמת in the correct order. Creation as a whole is planted throughout with seeds of אמת everywhere but it is hiding behind nature and you have to seek and toil to unscramble its letters. However on Shabbos, the neshama yesairah spoon feeds us to the point that אמת screams out. One just has to open his eyes and see it glaring straight at him.