Our Lord said this in order to afford us an image of our resurrection. For that which is handled is the body. But in our bodies we shall rise again. But the former is more subtle, the latter more carnal, as being still mixed up with the qualities of earthly corruption. Not then by His incorporeal nature, but by the quality of His bodily resurrection, Christ passed through the shut doors.
Reproduced in full. Translation: Oxford 1841 (Newman), public domain (Public domain).