According to Hebrews 3:10-11 and Psalm 95:10-11, the former Hebrew slaves wandered in the wilderness during the exodus for forty years before their children entered Israel–the promised rest. In Hebrews 3-4, Paul likens the forty-year interval in which the Hebrew slaves wandered in the desert and the subsequent rest their offspring received in the promised land to the life of the Christian saints on earth as they await the resurrection—the promised rest of the saints.
Interestingly, there appears to have been precisely forty years from the start of Jesus’ earthly ministry to the start of the siege of Jerusalem and the resurrection of the dead at the seventh trumpet. Biblical and historical evidence suggest that Jesus most likely began His ministry around Tishri of A.D. 29. See Daniel 9:24-27 Commentary: Daniel 9 Miraculously Fulfilled! The siege of Jerusalem and the resurrection of the dead began, I believe, in Nisan of A.D. 70. This is an interval of forty years and six months. In other words, Christianity was forty years old by the time of the resurrection—when the Christian saints wandering in the wilderness finally received their promised rest. Is this a coincidence?