Peter probably means here that Christ died in order to create a close relationship between us and God. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Here "flesh" refers to Christ's body; Christ was physically put to death. This can be stated in active form. Alternate translation: "People put Christ to death physically" (See: [[rc://en/ta/man/translate/figs-metaphor]] and [[rc://en/ta/man/translate/figs-activepassive]])
Possible meanings are 1) the Holy Spirit made Jesus alive. Alternate translation: "the Spirit made him alive" or 2) Jesus now had a spiritual body that would never die. Alternate translation: "he was made alive in the spirit" or "he was made alive with a spiritual body"