The Holy King David merited to kill Goliath, who was a manifestation of evil.
How did King David overcome the evil giant?
He understood from the "Shemah" the secret power of the holy unification of Hashem:
"SHEMA YISRAEL HASHEM ELOKENU HASHEM -- ECHAD."
Five HOLY WORDS that conclude with "ECHAD."
King David drew five stones from the river, and they miraculously melted into one stone. He had the intention to sanctify HaShem with the five stones and nullify the evil of Goliath. He hurled the stone at Goliath, and it penetrated his forehead.
Correspondingly, King David produced the Book of Tehilim, which is one book, comprised of five individual sections. This structure is similar to the five words of Shema and the final word, Ehad.
HaShem loves the Book of Tehillim as much as He loves the holy Torah!
Even though the Book of Tehillim is somewhat less holy than the Torah, the commonality between them is that they were both expressed from Ruach HaKodesh. Just as the entire Torah embraces the Names of HaShem, so too, the holy Book of Tehilim is totally comprised of the Names of HaShem.
The enormous popularity of Tehilim speaks for itself. Even though we understand a bare minimum of its secrets, it's tremendous following demonstrates the vast majority of mysteries that are beyond our comprehension.
Be inspired to say Tehillim every day and utilize its holiness to overcome negativity!
(Based on the commentary of Rabbi Moshe Dovid Valli)
