The imperative mood is used to express a command, entreaty, or prohibition. In English the imperative is used only with the second person (e.g., [You] get in the car!). The Greek imperative occurs in the present and aorist tenses. Both second and third person (“Let him/her/it do something”) forms may be used.

The imperative mood is built from both the present and the aorist stems. The present denotes action as a process in progress (“continue loosing”) and does not necessarily refer to the present time. The aorist form portrays action as a complete whole ([you] loose) (Mathewson, 34). The two tense forms (present/aorist) will often be translated the same way in English but one should be aware of the untranslatable differences between the two.  

The form of the second person singular must be learned for each tense. The second person plural form is the same as the present active indicative. You will have to use context to distinguish the two. The third person singular replaces the final ε of the second person plural with an ω. The third person plural replaces the second person plural ε with ωσαν. A handy way to learn the imperative endings is by learning them in a rhythmic manner: (do as a rap softshoe) (E-toe-ti-toe-san, ou -stho, sthe, sthosan [with a lisp], etc.).

Chant:  Imperative Endings tap-dance

Present/Process Action in Progress Imperative of λύω

Pedantically one may translate it “you continue loosing,” or “let her continue loosing.”

Note: The third person singular form replaces the final ε of the second person plural form with an ω, while the third person plural form replaces it with ωσαν.

First Aorist/Wholistic Complete Action Imperative of λύω
          -- you loose, let her loose

Second Aorist/Wholistic Complete Action Imperative of λείπω
    (I leave)

Imperative of εἰμί

Translated:  you be, she must be...

Imperatives are used in several ways:

1.   As a command:

ἀγαπᾶτε τοὺς ἐχθροὺς ὑμῶν.
Love your enemies! (Mat. 5:44).

2.   As a prohibition:

Μὴ φοβοῦ, τὸ μικρὸν ποίμνιον.
Fear not, little flock! (Lk. 12:32).

   Mounce (Basics, 307f.) observes that a prohibition may also be made in several other ways:

(1) οὐ + indicative (you shall not . . .)

(2) μὴ + aorist subjunctive

(3) οὐ μὴ + aorist subjunctive (strong negation)

3.   As an entreaty, especially when speaking to a superior (Dana and Mantey, Manual Grammar, 175f.; Summers, Essentials, 127):

Πάτερ ἅγιε, τήρησον αὐτοὺς ἐν τῷ ὀνόματί σου.
Holy Father, keep them in your name (Jn. 17:11).

λέγει αὐτοῖς,  Ἔρχεσθε καὶ ὄψεσθε. ἦλθαν οὖν καὶ εἶδαν.
He said to them, “Come, and you will see.” They came therefore and saw (Jn. 1:39).

λέγει αὐτῷ ὁ  Ἰησοῦς, Πορεύου, ὁ υἱός σου ζῇ. ἐπίστευσεν ὁ ἄνθρωπος.
Jesus said to him, “Go, your son lives.” The man believed (Jn. 4:50).

λέγει αὐτῷ ὁ  Ἰησοῦς,  Ἔγειρε ἆρον τὸν κράβαττόν σου καὶ περιπάτει.
Jesus said to him, “Arise, take your bed and walk” (Jn. 5:8).