Translation
in which
Go to footnote numberalso, he preached, having gone
Go to footnote numberto the spirits in prison,
Go to footnote numberParaphrase
It was in a spirit state, without a body, and through the power of the Holy Spirit of God, that he proclaimed the truth when He went to those whose spirits are now being held in prison,
Footnotes
1: "in which"
Here is where the double meaning of the word “spirit” is noticed. While the first usage of it in verse 19 seems to point to the Holy Spirit, this usage can easily point to both of the primary ideas conveyed by the word “spirit”, i.e. the spirit that God gives each person, which Paul called the “inner man” and God’s Holy Spirit.
2: "having gone"
This is the word for “go, walk, travel, traverse, journey, depart, go forth, go away.” The middle and passive forms, such as the passive participle used here, had already taken on what seems to us like an active meaning, “to go” rather than “to be transported”. So the point is that Jesus, in spirit form, went there.
3
See my comment about the imprisoned spirits after the next verse.