Or HaChaim on Genesis 1:28/אור החיים על בראשית א׳:כ״ח

1And He blessed them: The explanation is that He will not destroy the human specie. And he said, etc.: [by which] He commanded him to be fruitful and multiply; [such that] even if He blessed them that the human specie should continue, they should [still] not slack off from being fruitful and multiplying as a result of this. And I have seen faulty opinions among the creatures, from the children of our people, [that posit] that when there are three or four brothers, one or two of them should make efforts to be fruitful and multiply; and they say that this is [sufficient] for the perpetuation of the specie. And also with one man, when he has [already] perpetuated the specie, this logic comes [to suggest] that he should not put forth more efforts to be fruitful and multiply. For this [reason], God stated [at the beginning of His word, the pure commandment of God and stated, "be fruitful and multiply" and He did not make a limit to the commandment, and [that they are commanded] even if He blessed them that the human specie should not be destroyed from the world; and He finished and stated, "and fill the world." And it stated, "and conquer it" adjacent to "and fill" to say that by way of filling the earth, it will be conquered in front of them; as man does not govern over a deserted place, since from the angle of its desolation, it fills up with man's antagonists. It also wanted [to teach] by stating, "and He blessed them," that they would have the facility to reproduce and afterwards, He commanded them about the matter.