I verily thought with myself (εγω μεν ουν εδοξα εμαυτω). Personal construction instead of the impersonal, a touch of the literary style. Paul's "egoism" is deceived as so often happens.

I ought (δειν). Infinitive the usual construction with δοκεω. Necessity and a sense of duty drove Paul on even in this great sin (see on Acts 23:1), a common failing with persecutors.

Contrary (εναντια). Old word (adjective), over against, opposite (Acts 27:4), then hostile to as here.