I cannot lie by simply saying something false. I must have the intention to deceive. That is perfectly clear. Rather less obvious is that to tell the truth it does not suffice to say something true: I must also have the intention to be truthful.
"He told the truth but he wasn't being truthful" is not a contradiction. This is no more a contradiction than "He said something false but he wasn't intending to deceive." But how could one tell the truth without being truthful? One way is by saying something that happens to be true while intending to deceive. Another way is by saying something true to distract the hearer from the salient issue. A third way is by saying something true but omitting other truths relevant to the contextualization and understanding of the first.
Suppose the following sentence is true: "Jane shot Sam several times in the chest with a .45 caliber pistol after he came at her with a knife threatening to rape her." Someone who assertively utters the first independent clause while omitting to utter the second has said something true without being truthful.
In sum, one can say what is false without being untruthful and one can say what is true without being truthful.
Persons, not propositions, are truthful or the opposite. Propositions, not persons, are true or the opposite.
And yet there is some connection between truth and truthfulness.
Here is a mere outline of an argument. In a world without mind there could be no truth. For truth is some sort of correspondence or adequation of mind and world. There are no free-floating truths, no Wahrheiten an sich. Truth is moored in mind. But truth is absolute: it transcends the contents and powers of finite minds. The true is not what you or I believe or what all of us believe. Nor is the true the believable. The true is not the rationally acceptable, not even the rationally at the ideal limit of inquiry. The true is not the warrantedly assertible. There no viable epistemic/doxastic analysis of the truth predicate. And yet truth involves mind. Enter divine mind. The truth is grounded in the divine truthfulness. In God, truth and truthfulness colaesce.
Well, I warned you that it was a mere outline. Brevity is the soul of blog.