Perish with thee (sun soi eiē eis apōleian). Literally, Be with thee for destruction. Optative for a future wish. The use of eis with the accusative in the predicate is especially common in the lxx. The wish reveals Peter’s indignation at the base offer of Simon. Peter was no grafter to accept money for spiritual power. He spurned the temptation. The natural meaning of Peter’s language is that Simon was on the road to destruction. It is a warning and almost a curse on him, though Act 8:22shows that there was still room for repentance.
To obtain (ktāsthai). To acquire. Usual meaning of the present tense (infinitive middle) of ktaomai.