To be or not to be

An interesting observation came up in a greek reading group yesterday. We were reading in the sermon on the mount at Matthew 5:48. Here is the Greek text:

ἔσεσθε οὖν ὑμεῖς τέλειοι ὡς ὁ πατὴρ ὑμῶν ὁ οὐράνιος τέλειός ἐστιν.

The question is concerning ἔσεσθε which is a future middle indicative 2nd plural from εἰμί.
Many translations treat this as a command or imperative with, "Be ye, therefore, perfect...,"
but should it rather be treated more as a result? "Ye, therefore, will be perfect..." or even "You, then, will be perfect..."

Are there any syntactical or grammatical reasons for treating this future middle as an imperative?
Commentaries I've looked at so far seem to assume one treatment or the other without dealing with the grammatical question.

John 1:12

ὅσοι δὲ ἔλαβον αὐτόν, ἔδωκεν αὐτοῖς ἐξουσίαν τέκνα θεοῦ γενέσθαι, τοῖς πιστεύουσιν εἰς τὸ ὄνομα αὐτοῦ,

ὅσοι relative pronoun "as many as"

δὲ post positive conjunction "and" or "but"

ἔλαβον verb aorist active indicative 3rd plural from λαμβάνω "received"

αὐτόν personal pronoun accusative masculine singular "him"

ἔδωκεν verb aorist active indicative 3rd singular from δίδωμι "he gave"

αὐτοῖς pronoun dative plural "to them"

ἐξουσίαν noun accusative feminine singular "authority"

τέκνα noun nominative neuter plural "children"

θεοῦ noun genitive masculine singular "of God"

γενέσθαι verb aorist middle infinitive from γίνομαι "to become"

τοῖς defininte article dative masculine plural "the"

πιστεύουσιν verb present active participle dative masculine plural (note the attributive position of this participle. It is describing the "them" of αὐτοῖς.)

εἰς prepostion with accusative case "in" or "into"

τὸ definite article accusative neuter singular "the"

ὄνομα noun accusative neuter singular "name"

αὐτοῦ personal pronoun genitive masculine singular "of him"

Rough Translation:

as many as but received him he gave to them authority children of God to become the believing in the name of him

Smooth Translation:

But as many as received him, to them he gave authority to become children of God, the ones believing in his name.

John 1:11

εἰς τὰ ἴδια ἦλθεν, καὶ οἱ ἴδιοι αὐτὸν οὐ παρέλαβον.

εἰς preposition accusative "into"

τὰ definite article nominative neuter plural "the"

ἴδια noun nominative neuter plural "one's own things"

ἦλθεν verb aorist indicative 3rd singular from ἔρχομαι "he came"

καὶ conjunction "and"

οἱ definite article nominative masculine plural "the"

ἴδιοι noun nominative masculine plural "his own (people)"

αὐτὸν pronoun accusative masculine singular "him, himself"

οὐ negative particle "not"

παρέλαβον verb aorist active indicative 3rd plural from παραλαμβάνω "they received"

Rough Translation:

into the one's own things he came and the his own himself not they received

Smooth Translation:

He came to his own things and his own people did not receive him

John 1:10

ἐν τῷ κόσμῳ ἦν, καὶ ὁ κόσμος δι' αὐτοῦ ἐγένετο, καὶ ὁ κόσμος αὐτὸν οὐκ ἔγνω.

ἐν preposition dative "in"

τῷ definite article dative masculine singular "the"

κόσμῳ noun dative masculine singular "world"

ἦν verb imperfect indicative 3rd singular from εἰμί "(he) was"

καὶ conjunction "and"

ὁ defininte article nominative masculine singular "the"

κόσμος noun nominative masculine singular "world"

δι' elided preposition with genitive "through"

αὐτοῦ personal pronoun genitive masculine singular "him"

ἐγένετο verb aorist middle indicative 3rd singular from γίνομαι "came to be"

καὶ correlating conjunction "but"

ὁ definite article nominative masculine singular "the"

κόσμος noun nominative masculine singular "world"

αὐτὸν personal pronoun accusative masculine singular "him"

οὐκ negative particle "not"

ἔγνω verb aorist active indicative 3rd singular from γινώσκω "he (or "it" - the world) knew"

Rough Translation:

in the world he was and the world through him came to be and the world him not it knew

Smooth Transaltion:

He was in the world and the world came to be through him, but the world did not know him.