Believing on him is not here to be understood strictly of saving faith; but rather, of some preparations toward it: they began to believe that he was the true Messias, and to have more honourable thoughts than they had of him: that this was all, will appear from what we find in the following verses; and believing often signifieth no more in the New Testament than a light assent given to some propositions of the gospel relating to Christ.
Related Commentaries of John 8:30
John 8:30
30 As he spake these words, many believed on him.