When it was said concerning the old world before the flood, "My Spirit shall not always strive with man," it is implied, it had been constantly and generally striving, until then; but that it was now time, by the holy, wise, and righteous judgment of Heaven, to surcease, and give them over to the destruction which ensued. Which text, 'tis true, some interpret otherwise; but if we will allow that of the 1 Pet. iii. 18, 19, 20, to mean that, while Noah, that preacher of righteousness, did it externally, Christ was, by his Spirit, inwardly preaching to that generation, who were now since in the infernal prison; not while they were so, (which the text says not,) but in their former days of disobedience on earth; this place will then much agree with the sense, wherein we (with the generality of our interpreters) take the other.John Howe, "The Living Temple," in The Works of the Rev. John Howe (New York: John P. Haven, 1838), 1:105.
One can see that John Howe agrees with John Flavel on this passage. He's saying that while Noah was preaching externally to disobedient sinners, Christ was, by His Spirit, preaching through him to that generation. As a result of their disobedience, they are now shut in prison and awaiting final judgment, especially for sinning against such patient "strivings" of the Spirit. The text is not saying that Christ in his intermediate state (between the time of his death on the cross and his resurrection) went and preached to spirits in prison.