Srila Prabhupada in one poem described as the perfection of mantras one statement by Arjuna "karisye vacanam tava"
arjuna uvāca
naṣṭo mohaḥ smṛtir labdhā
tvat-prasādān mayācyuta
sthito 'smi gata-sandehaḥ
kariṣye vacanaḿ tava
Arjuna said: My dear Kṛṣṇa, O infallible one, my illusion is now gone. I have regained my memory by Your mercy. I am now firm and free from doubt and am prepared to act according to Your instructions.
vedabase.net/bg/18/73/
The karisye vacanam tava part means "I am now prepared to act according to your instructions".
This is the perfect mantra, if when we say it we really mean it.
arjuna uvāca
naṣṭo mohaḥ smṛtir labdhā
tvat-prasādān mayācyuta
sthito 'smi gata-sandehaḥ
kariṣye vacanaḿ tava
Arjuna said: My dear Kṛṣṇa, O infallible one, my illusion is now gone. I have regained my memory by Your mercy. I am now firm and free from doubt and am prepared to act according to Your instructions.
vedabase.net/bg/18/73/
The karisye vacanam tava part means "I am now prepared to act according to your instructions".
This is the perfect mantra, if when we say it we really mean it.