They were much perplexed (diēporoun). Imperfect active of diaporeō old verb by Luke only in the N.T. See note on Act 2:12. They continued puzzled.
Whereunto this would grow (tōi an genoito touto). More exactly,
As to what this would become. Second aorist middle optative of ginomai with an, the conclusion of a condition of the fourth class (undetermined with less likelihood of determination), the unexpressed condition being “if the thing should be allowed to go on.” The indirect question simply retains the optative with an (Robertson, Grammar, pp. 1021, 1044). If they had only known how this grain of mustard seed would grow into the greatest tree on earth and how dwarfed the tree of Judaism would be beside it!