What's vague? Let me try to spell this out in excruciating detail:

Making good on one's commitments promotes the virtue of integrity.
Integrity is constitutive of good character.
One cannot consistently act as a person of good character without having it.
To act ethically is to act as a person of good character does.
Ethics specifies what one has most reason to do or want.

So, if you ask me what I have most reason to do in a circumstance where I've made a commitment, ceteris paribus, I'll respond that I'll make good on my commitments.