Why did the resurrected saints come out of their graves after Jesus rose instead of before?
They came out after His resurrection because Christ had to be the first to be resurrected; He is the firstfruits. Only then could other examples of resurrection follow, fulfilling the sheaf analogy. These resurrected believers, given immortality, were taken up into heaven.
Les explains that they did not come out of the grave while He was on the cross, but after He had been resurrected Himself. Christ had to be the first to ever be resurrected. Then, to make the sheaf analogy come to the full, there had to be other examples of resurrection. So some Jewish believers were evidently resurrected from the cemeteries around Jerusalem, came into the city, and appeared probably to their friends and relatives. Since Scripture is silent, Les assumes that because Christ in His resurrected body ascended into heaven, these saints did as well. These were not like Lazarus, who came back to die again; they were resurrected believers given immortality, and no doubt were taken up into heaven. That makes the sheaf of the first fruits, the beginning of the first resurrection.