The huge open-loop gain of op-amps (at least one billion in the case of the OPA357) makes them virtually unusable as amplifiers without some form of feedback network to lower the gain to a reasonable and predictable value. There is one exception where are used in open-loop mode, and that is as comparators. Any minute difference between IN+ and IN- gets amplified so much that it saturates the output either close to the positive rail or to the negative one.