When Scripture quotes Scripture: its kind of like God saying “because I said so”.

Beside what greater authority to appeal to then God and what more truthful source than He to trust anyhow.

“For when God made promise to Abraham, because he could swear by no greater, he sware by himself….For men verily swear by the greater: and an oath for confirmation is to them an end of all strife.” – Hebrews 6:13,16