What is the ruling on one who dedicates himself to Allah in worship, yet is ignorant of the rulings concerning vows (nadhr), and is unable to fulfill it? Is he obligated to offer expiation for breaking an oath (kaffarat yamin)? And does the expiation multiply if he breaks it again?

The statement mentioned is not considered an explicit vow (nadhr) nor one of its allusions, especially since the questioner did not intend a vow and was unaware of its implications. Consequently, no expiation is required for falling short in acts of obedience. Rather, this statement is intended to encourage righteous deeds.