619 Ὅστις with an indicative often suggests cause, purpose, or result, by treating a definite antecedent as indefinite in order to characterise it (generally of persons):

Ti τὸν θεοῖς ἔχθιστον οὐ στυγεῖς θεόν, ὅστις τὸ σὸν θηντοῖσι προύδωκεν γέρας why dost thou not hate this god, to gods most hateful, one who betrayed thy prize to men? A. PB. 38.

Πρεσβείᾱν πέμπειν ἥτις ταῦτʼ ἐρεῖ to send an embassy to say this. D. I, 2.

Tίς οὕτω μαίνεται ὅστις οὐ βούλεταί σοι φίλος εἶναι who is so mad as not to wish to be your friend? AN. II. 5, 12.