"He who is faithful in what is least is faithful also in much; and he who is unjust in what is least is unjust also in much."
Luke 16:10
In the Greek, the word for 'faithful' is the same word for 'faith.'
In English, we say that 'fruitful' means 'full of fruit',
'joyful' means 'full of joy'.
In the same way 'faithful' means 'full of faith'.