Luke 13:24

Ἀγωνίζεσθε εἰσελθεῖν διὰ τῆς στενῆς θύρας, ὅτι πολλοί, λέγω ὑμῖν, ζητήσουσιν εἰσελθεῖν καὶ οὐκ ἰσχύσουσιν,

Rough Word-by-word:
Strive to enter through the narrow door, because many, I say to you, they will seek to enter and not they will be strong,

Smooth Translation:
Strive to enter through the narrow door, because many, I say to you, will seek to enter and they will not be able.

Notes:
The difficulty stands out here. This is not a promise of ease, but a promise of struggle. There is a need for strength. I don't believe our Lord would give us an imperative of an impossibility, however, so there is hope in putting forth effort.

Ἀγωνίζεσθε present middle imperative 2nd plural from ἀγωνίζομαι (I struggle, I strive) "You all struggle"

εἰσελθεῖν aorist active infinitive from εἰσέρχομαι (I go in, I enter) "to enter"

διὰ preposition with genitive "through"

τῆς definite article genitive singular feminine "the"

στενῆς adjective genitive singular feminine "straight, narrow" (note: stenosis of the arteries is narrowing of the arteries)

θύρας noun genitive singular feminine "door"

ὅτι conjunction "that, because"

πολλοί adjective nominative plural masculine "many"

λέγω verb present active indicative 1st singular from λέγω (I say) "I say"

ὑμῖν pronoun dative 2nd plural "to you"

ζητήσουσιν verb future active indicative 3rd plural from ζητέω (I seek) "they will seek"

εἰσελθεῖν verb aorist active infinitive from εἰσέρχομαι (I go in, I enter) "to enter"

καὶ conjunction "and"

οὐκ adverb of negation "not"

ἰσχύσουσιν verb future active indicative 3rd plural from ἰσχύω (I am strong, I am able) "they will be strong"