In Deuteronomy 6:4-9 it is written:
Hear O Israel, the Lord is our God, the Lord is One. You must love the Lord your God with all your heart and with all your soul and with all your might. Take these words with which I command you this day. Impress them upon your children and recite them, when you stay at home and when you are on your way, when you lie down and when you get up...
Shema Israel prayer is the most known prayer in Judaism. The source of the sentence is from Jacob who is named Israel. When Jacob was about to die he called upon his sons and swore them to continue believing in the one G-d. The meaning of this prayer is: Hear O Israel, meaning hear Jacob; our G-d is the one G-d.
It is interesting to see that Israel's sons are instructed to love G-d. The numeric value of the word AHAVA (love, which is the essence of the whole creation) is 13. The word EHAD (one) also has a numeric value of 13 and the testimony of Jacob and sons is said in the presence of 13 people (Jacob and his sons).
One more interesting thing is that the name "Israel" is composed of the names of all the patriarchs and matriarchs (in full writing) and adds up to the number 13 in gematria (the science of Hebrew letters in which the letters have numeric value)…