Now when he was in Jerusalem at the passover, in the feast day, many believed in his name, when they saw the miracles which he did.
Now when he was in Jerusalem at the Passover, in the feast [day], х en (G1722) tee (G3588) heortee (G1859)] - rather, 'during the feast,' which lasted seven days. What is now to be related is not the result of one day, but of the whole period of this festival. The cleansing of the Temple, recorded in the preceding verses, occurred probably before the feast began.
Many believed in his name - see the note at John 1:12. These converts, persuaded that His claims were well founded, reposed trust in Him in that sense, and to that extent "when they saw the miracles which he did."
When they saw the miracles which he did. What these were is not here recorded; nor can we get any light from the other Evangelists, as they speak of no pubic visit to Jerusalem but the last. It is singular that none of these miracles are recorded, since in the very opening of the next chapter Nicodemus refers to the immense force of conviction which they carried (John 3:2), and they are again referred to in John 4:45.