The Perfection of Truthfulness - Truthfulness has several meanings

The perfection of panna should be developed together with the other perfections. We cannot forego any of the perfections, because each perfection is a necessary support for the others. Truthfulness, sacca, for example, is necessary for the performing of generosity, dana. Without truthfulness generosity cannot reach fulfilment. Without truthfulness the observance of síla cannot reach accomplishment. Thus, truthfulness is essential for the fulfilment of the other perfections.
We read about the meaning of truthfulness in the “Paramattha Jotika”, the Commentary to the “Sutta Nipata”, The Group of Discourses, I, The Snake Chapter 10, Alavaka:

“The term sacca has several meanings: 

it can mean truthfulness in speech (vaca sacca),

or it can mean truthfulness in abstaining (virati sacca).

It is steadfastness in the truth,

in the abstention from akusala kamma.

 

It can mean truthfulness of view (ditthi sacca),

truthfulness as to right view.

Sacca can also refer to brahmana sacca (brahmin truths),

paramattha sacca (ultimate truth) and ariya sacca (noble Truths).

The term ‘saccena’ (by truthfulness), means, someone acquires a good
reputation,

because he speaks the truth, because of sincerity.

The Buddhas, Pacceka Buddhas and the ariyan disciples have a high reputation

because of ultimate truth, paramattha sacca.”
Only panna can understand the true nature of each dhamma. However, the development of panna is conditioned by listening to the Dhamma, and by considering it in all details. One should develop panna gradually, stage by stage.
We still have defilements, but we listen to the Dhamma and we have taken refuge in the Dhamma during this life. This shows that we are following the way to develop panna, so that the characteristics of realities that are appearing now can be penetrated. We should follow in the footsteps of the Bodhisattas and accumulate the perfections.
People say that they want to practise the Dhamma. The practice of the Dhamma is the abandoning of akusala: of lobha, dosa and moha. Lobha should be abandoned when it arises, that is the practice of the Dhamma.
If someone wants to apply the Dhamma he should not delay this. When anger arises, one should abandon it so that there is non-hate, that is the practice of the Dhamma. When jealousy, stinginess or other kinds of akusala arise one should abandon them, that is the practice of the Dhamma. However, defilements cannot be eradicated according to our wishes or expectations. Even the Bodhisatta who had accumulated the perfections during innumerable lives was still susceptible to the power of akusala, because he had not yet eradicated defilements.