The study of numbers:
[Genesis 21:29-31 KJV]
29 And Abimelech said unto Abraham, What [mean] these seven ewe lambs which thou hast set by themselves?
30 And he said, For [these] seven ewe lambs shalt thou take of my hand, that they may be a witness unto me, that I have digged this well.
31 Wherefore he called that place Beersheba; because there they sware both of them.
"Sheba" means both "7" and "to swear" showing that numbers have spiritual meanings as well.