From the cover (itself) shall you make the cherubim (Ex. 25:19)
The cherubim were made with the faces of small children, one a boy and one a girl. From this we learn that providing the proper Jewish education for even our tiny children is a basic principle necessary for our keeping the Torah.
(Rabbi Yosef Ber of Brisk)
Within and without shall you overlay it (Ex. 25:11)
A true Torah scholar is one whose "inside" matches his "outside." Merely learning the lofty principles contained in the Torah is not enough - its lessons must also be internalized.
That is why we say in Psalms (45:14), "All the glory of the king's daughter is within." The splendor and glory of the Torah is the internal purity it leads to.
(Kiflayyim L'Toshiya)
Of a talent of pure gold shall it be made (Ex. 25:39)
Man's purpose in life is to illuminate his surroundings with the light of Torah and mitzvot. This responsibility holds true no matter what the individual's circumstances or mood may be.
The numerical equivalent of the Hebrew word for talent, "kikar," is 140 - the same as the numerical equivalent of "mar" (bitter), and "ram" (lofty). No matter what our situation, our task remains the same.
(the Previous Rebbe)
Two and one-half cubits its length, and a cubit and a half its breadth, and a cubit and a half its height (Ex. 25:10)
The ark was measured in fractions, not whole numbers, teaching us that to achieve spiritual growth, one must first "break down" and shatter one's negative characteristics and bad habits.
(Sefer Hamamarim U'Kuntreisim, the Previous Rebbe)