What does it mean to be absent from the Lord while at home in the body?
It means that while a believer is alive and at home on this planet in the body, he is bodily absent from the Lord. That absence is physical, not spiritual, because the soul and spirit are already redeemed, made citizens of heaven, and cannot be in both places at once.
Les explains II Corinthians 5:6 in contrast with the spiritual reality. While we are at home in the body—alive on the planet—we are absent bodily from the Lord, since we cannot be in both places. Yet spiritually, in the invisible realm, we are already citizens of heaven; Colossians says we have been translated into the kingdom of His dear Son. The soul and spirit are redeemed at salvation, but the body awaits its redemption, guaranteed by the indwelling Holy Spirit as God's down payment, until it is reunited with soul and spirit in a new body for eternity.
Therefore we are always confident, knowing that, whilst we are at home in the body, we are absent from the Lord: