Lam or lamed is the twelfth of twenty-two letters meaning that it sits squarely in the center of the aleph-beis. As others have pointed out, this makes lam the heart of the aleph-beis just as our human heart is the center of our own bodies. Lam is also the largest letter, physically, making it the Supreme King.
Lam, as one of the two letters of the name of god, EL, connects it to concepts of supremacy and power.
The shape of the ancient letter lam is a shepherd’s staff that was used to guide sheep: 
Fabre d’Olivet in his opus, “The Hebrew Tongue Restored” written in 1921 writes about a beautiful dimension of lam (pg 377): “As a symbolic image, it represents the arm of man, the wing of a bird that which extends, raises and unfolds itself. As a grammatical sign, it is expansive movement and is applied to all ideas of extension, elevation, occupation, possession.”
Lam is the staff of authority, the heart of hearts, the supreme king, the principle of expansion, and not uncoincidentally, the second letter of the two letter name of god – El. It is, in summation the quintessential letter which stands for divinity and the stuff of the heavens.
