Charles Ellicott Commentary John 20:9

"For as yet they knew not the scripture, that he must rise from the dead." — John 20:9 (ASV)

For as yet they did not know the scripture.—This explains in what sense it was that Saint John now believed. Up to this time they did not know the meaning of the Scripture which foretold the Resurrection; but from that moment at least they recognized in the fact of the absent body of Christ the truth that He must rise again. (Compare Notes on John 2:21-22.)

That he must rise again from the dead.—Compare especially Notes on Luke 24:26; Luke 24:44.