These two letters are the "first and the last," the "beginning and the end" and the "Aleph and the Tav" (which is translated as "the alpha and the omega," the first and last letters of the Greek alphabet, in the book of Revelation chapter 22 (the last chapter of the bible)).
13 I am the Alpha and the Omega -- the Beginning and End -- the First and the Last.
The modern Hebrew form of the letter aleph is א, but is an evolved form of the original pictograph , a picture of an ox head.
The ancient pictographic form of the letter ת is , a picture of two crossed sticks which are used as a marker.
When these two pictographs are combined we have the meaning "an ox toward the mark."
Fields were plowed with a plow pulled behind an ox (or pair of oxen). In order to keep the furrows straight the driver of the ox would aim toward a mark, such as a tree or rock outcropping in the far distance.
As we can see, this meaning of driving the ox toward a mark, can be seen in the letters of the Hebrew word את (et).
The word את is also used very frequently (over 7,000 times) in the Hebrew language such as can be seen in the very first verse of the Bible.
Because the word את has no equivalent in the English language, it is not translated, but to demonstrate its meaning in this verse I will translate Genesis 1:1 into English, but retain the word את in its center position.
1 In the beginning God createdאת
the heaven and the earth.
KJV Old Testament Hebrew Lexicon
Just as the phrase "heaven and earth" is an idiomatic expression meaning "all of creation," the phrase "aleph and tav" is an expression meaning "the first and the last." Ancient Hebrew Research Center source link: http://www.ancient-hebrew.org
The upper-case letter Π is used as a symbol for: