Paul takes us all the way back to Leviticus 23 and the inauguration of the Feast of Firstfruits, where the very first sheaf of grain in every smallholding, every farm in ancient times, was to be brought to the priest and the priest would wave it in the air. This was before the main harvest; the rest of the harvest was brought in later, and the end of harvest was marked by the Feast of Weeks seven weeks later (Leviticus 23:15-22).
Some texts show that God the Father had a part in the resurrection; some texts show that God the Holy Spirit had a part in it, but the majority tell us that the Saviour raised himself, and it was by his power. So while every member of the Godhead has some part in it, we know that it was also the Lord himself by his mighty power that raised himself from the dead. His eternal consciousness tasted death for us, and experienced the agony and pain of separation from God. He experienced the attacks of the demons, hemming him around, trying to keep him in the domain of death. But Christ, though truly dead, when the moment came by an exertion of his mighty and amazing power shattered and broke the bands of death for every one of us.
Sleep does not refer to the soul, but to the body. All those people who believe in Christ, who love him and trust in him; all those who belong to God, when they die, their bodies, of course, perish and rot; but their bodies are said to sleep. They are not asleep, literally; of course not. They are dead, as the apostle goes on to affirm shortly. Nevertheless, sleep is the appropriate term, because one day they will be raised again. Christ used the same figure in describing Lazarus: ‘Our friend Lazarus sleepeth; but I go, that I may awake him out of sleep. Then said his disciples, Lord, if he sleep, he shall do well. Howbeit Jesus spake of his death’ (John 11:11-13). But it doesn’t refer to the soul, because at death the soul of the believer goes to the paradise of Christ, awaiting that coming final day of resurrection.