The Key

Imām Ibn Taimiyyah, may Allāh have mercy on him, said:

Truthfulness is the key to all goodness just as lying is the key to all evil. It’s because of this, they say about one of the shaikhs that he asked one or another among his companions to repent, [saying]: “I’m not going to exhort you to anything other than to be truthful.”

So they thought about that and found that truthfulness gives rise to all goodness.

Al-Istiqāmah, vol. 1, p. 467.