PERIPHRASTIC FORM OF THE IMPERFECT
Periphrastic Imperfects, formed by adding a Present Participle to the Imperfect of the verb eivmi,, are frequent in the New Testament, especially in the historical books. The large majority of these forms denote continued action.
Mark 10:32; καὶ ἦν προάγων αὐτοὺς ὁ Ἰησοῦς, and Jesus was going before them. So also Luke 1:10, 22; John 13:23; and probably Mark 2:18. In a few instances repeated action is referred to, as Luke 5:16; 19:47; Gal. 1:23. Cf. The Predicative Adjective Participle (3).