The content of what the other disciple believed is not indicated. Moreover, the affirmation that he believed causes difficulty in light of what is said in verse 9: They … did not understand the scripture which said that he must rise from death. But the most natural solution is that the other disciple believed that Jesus had been raised from the dead. This belief was based on his own observation of the empty tomb, rather than on the testimony of the scripture, which was another witness to the resurrection.

In some languages one cannot use such a verb as believed without indicating what was believed, for example, “he saw and believed that Jesus had risen from the dead” or “he saw the cloths lying there and therefore believed that….”

Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .