"Heart" here is a metonym for "thoughts and intentions." AT: "love one another earnestly and completely" or "love one another earnestly with right thoughts and good intentions" (See: [[rc://en/ta/man/translate/figs-metonomy]])
# born again, not from perishable seed, but from imperishable seed
Possible meanings are that Peter speaks of the word of God either 1) as the seed of a plant that grows and produces new life in believers or 2) as the tiny cells inside a man or woman that combine to cause a baby to grow inside the woman. (See: [[rc://en/ta/man/translate/figs-metaphor]])
Peter speaks of God's word as if it were alive forever. In reality, it is God who lives forever, and whose instructions and promises last eternally. (See: [[rc://en/ta/man/translate/figs-metonymy]])