Al-istitbāʿ praises a subject through one quality in a manner that entails another praiseworthy quality. The first is the stated praise; the second is a commendable implication of it.
This is not merely listing two virtues of the same person. The latter should follow meaningfully from the former.
For example, a ruler's justice may be expressed so as to imply the security and well-being of subjects. The second virtue is then a consequence of the first praise.