II Corinthians 5:8-9
8 We are confident, I say, and willing rather to be absent from the body, and to be present with the Lord.
9 Wherefore we labour, that, whether present or absent, we may be accepted of him.
When a believer in Christ’s body dies, he doesn’t actually die, but sleeps because, as these verses tell us, to be absent from the body is to be present with (at home with) the Lord. At the moment that the body of the believer dies, his spirit is present with the Lord. So when you compare this with what Paul says in I Thess. 4:13-18, we rejoice in the fact that at the moment you received Christ as your personal Savior, you will be in the presence of the Lord forever!