Exegesis:

agōnizesthe eiselthein dia tēs stenēs thuras ‘struggle to go in through the narrow door.’ The saying of entering the kingdom of God (cf. 18.17) is here modified by the picture of entering a house. The article tēs seems to imply that the phrase dia tēs stenēs thuras is a generally known saying. stenos.

agonizomai with the following infinitive, ‘to struggle,’ ‘to strive,’ ‘to strain every nerve.’

hoti polloi, legō humin, zētēsousin eiselthein ‘for many, I tell you, will try to get in.’ legō humin is inserted to emphasize polloi. For zētēsousin cf. on 5.18. eiselthein takes up eiselthein dia tēs stenēs thuras.

kai ouk ischusousin ‘and they will not be able.’ For ischuō cf. on 6.48.

Translation:

Strive, or, “do your utmost/best” (Phillips, Good News Translation), ‘try hard.’

To enter may require a goal, i.e. ‘the kingdom of God,’ anticipating v. 28.

By the narrow door, or, making explicit the concessive force, e.g. ‘how narrow the door may be.’ If the metaphor would be incomprehensible, one may say, ‘along the difficult path,’ ‘how difficult the way (to get in) may be.’ Narrow has been described as, ‘which hole/width-small’ (Trukese, Pohnpeian), or by a reciprocal form of ‘to close-in-on’ (Shona), or an adjective derived from ‘to squeeze through’ (West Nyanja).

For seek see 5.18.

Enter, or, ‘enter it,’ ‘get in there.’

And will not be able, or, filling out the ellipsis, ‘will not be able to enter (it), or, to do so.’

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.