He looked (εμβλεψας). First aorist active participle of εμβλεπω, antecedent action before λεγε (says).

As he walked (περιπατουντ). Present active participle in dative case after εμβλεψας and like ερχομενον in verse John 1:29 vividly pictures the rapture of John in this vision of Jesus, so far as we know the third and last glimpse of Jesus by John (the baptism, verse John 1:29, and here).

Saith (λεγε). Historical present, change from ιστηκε before. He repeats part of the tribute in verse John 1:29.