Exegesis:

In the form of a series of questions vv. 32-34 take up the theme of the love of enemies of v. 27 and, distinguishing it sharply from any form of mutual love or good treatment, lead clearly up to, and are contrasted with v. 35f.

kai ei agapate tous agapōntas humas ‘and if you love those who love you,’ conditional clause stating the case to which the following question applies. kai is best taken as connecting a new subject with what precedes.

poia humin charis estin? ‘what credit is that to you?’ poia is here equivalent to tis. For charis two interpretations are given, i.e. (1) ‘favour,’ i.e. with God or men, and (2) ‘credit,’ i.e. in the sight of God or in the judgment of men, preferably the latter.

kai gar ‘for even.’

hoi hamartōloi ‘sinners,’ cf. on 5.8. The article is generic.

Translation:

A passive construction may be idiomatically preferable here, ‘if (only) those who love you are loved by you,’ ‘if you love those by whom you are loved.’

What credit is that to you?, a rhetorical question anticipating a negative answer. The noun may be taken here in the sense of ‘appreciation/respect (to be won)’; hence, ‘what is there to-be-praised about you’ (Sundanese, similarly Sinhala), ‘you would be able to be thanked for what’ (Shona 1962, similarly Zarma, Cuyono); or of ‘merit (to be deserved),’ ‘reward (to be received)’; hence, ‘why do you think men/God should reward you for that,’ ‘God will not repay that type of loving-one-another’ (Tboli), ‘you would be able to deserve to be given what’ (Shona 1966).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.