Exegesis:

plēn agapate tous echthrous humōn ‘but love your enemies,’ contrasting with v. 32, as do the subsequent two commandments with vv. 33f. This shows that the subsequent commandments may be understood as applications of the commandment to love the enemies. For plēn cf. on v. 24.

mēden apelpizontes, ‘expecting nothing in return.’ apelpizō usually means ‘to despair’ (cf. L-Sc, s.v.) which would lead to a translation ‘despairing in no respect,’ i.e. “never despairing” (An American Translation, cf. New English Bible, Revised Standard Version footnote). But the context requires the meaning ‘to expect in return’ which appears only in later Greek.

kai estai ho misthos humōn polus ‘and your reward will be great,’ cf. on v. 23.

kai esesthe huioi hupsistou ‘and you will be sons of the Most High.’ The clause may specify the reward to which the preceding clause refers (cf. New English Bible), or refer to something different from that reward. The former is preferable (cf. Mt. 5.9 and 45).

For hupsistos cf. on 1.32. huioi hupsistou means ‘people having the same nature as the Most High,’ cf. Leaney.

hoti autos chrēstos estin ‘because he is kind,’ explaining why they will be sons of the Most High: “likeness proves parentage” (Plummer). autos ‘he,’ not ‘he himself.’ For chrēstos (here used of God) cf. on 5.39.

epi tous acharistous kai ponērous ‘towards the ungrateful and evil,’ looked upon as one group, as shown by the single article. acharistos.

Translation:

Expecting nothing in return, or, ‘and do not expect that anything will be given back to you, or, that you will receive anything back,’ cf. also, ‘I will get it back thought not thinking’ (Ekari). The verb is here virtually identical with ‘to hope.’

Sons of the Most High. The plural should be made explicit, in order to distinguish this phrase from the title of Jesus (1.32; 8.28). The phrase is preferably rendered literally, but it may be necessary to shift to a simile, ‘sons, as it were, of (or, comparable to sons of) the Most High.’

Kind, or, ‘friendly,’ ‘good,’ ‘good of heart’ (Tae,’ Sranan Tongo), ‘generous’ (Bahasa Indonesia).

The ungrateful and the selfish, or a construction as, ‘those who are ungrateful and wicked,’ ‘wicked people who don’t know gratitude’ (Sranan Tongo). Ungrateful, or, ‘not saying “Thank you” ,’ ‘not knowing gratitude/thanks.’ In Bahasa Indonesia thanks towards men is expressed by the phrase ‘to accept/acknowledge kindness,’ in Toraja-Sa’dan by a verb that has the basic meaning of well wishing (cf. on “hail” on 1.28), and in Tae’ by ‘to praise.’ — The selfish, preferably, ‘evil men,’ ‘the wicked.’

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.