It is not a value or a virtue among others, but it is that through which and for which there are values and virtues.
It is the virtue of memory because there is no thought without memory and without fighting against the risk of forgetting.
To be faithful to thought is not to refuse to change our ideas or to consider them absolutes, but it is to refuse to change without having good and strong reasons, it is to take as true what has been clearly and solidly judged. We have the right to change our minds, but only out of duty. Neither dogmatism nor inconstancy.
Fidelity to the truth first, then to the remembrance of the truth.
It is the principle of all morality, being the opposite of the inversion of values, of frivolous or self-interested versatility, renunciation, perfidy, or inconstancy.
Philosophy itself is an extreme fidelity to thought.