“This is how God showed his love among us: He sent his one and only Son into the world that we might live through him.” 1 John 4:9
“How God showed his love among us” was to visibly demonstrate it through Jesus’ work on the Cross on our behalf.
“One and only Son” expresses the sense of uniqueness, not a literal birth. John is the only NT author who calls Jesus this. In other words, Jesus is the unique Son of God; no other person is God’s Son in the way Jesus is.
“Live through Him” means believers live through Jesus Christ, who died, rose, and ascended into heaven so that He might fill all heaven and earth. He is present with all believers through His chosen means of grace: His Word, Holy Baptism, and the Lord’s Supper. The Word made flesh is our source of life, our mediator; we live only because of Him, as Jesus Himself taught.
God’s blessings on your day…