Hebrews 6 (RSV)Malachi 3:1
19 We have this as a sure and steadfast anchor of the soul, a hope that enters into the inner shrine behind the curtain, 20 where Jesus has gone as a forerunner on our behalf, having become a high priest for ever after the order of Melchiz′edek.
But this is in reference to Jesus. Do you know where else? Or would it be in the Greek OT?
Behold I send my angel (=messenger), and he shall prepare the way before my face. Malachi 4:5
Behold I will send you Elias the prophet, before the coming of the great and dreadful day of the Lord.Mark 17:10
And his disciples asked him, saying: Why then do the scribes say that Elias must come first? 11 But he answering, said to them: Elias indeed shall come, and restore all things. 12 But I say to you, that Elias is already come, and they knew him not, But have done unto him whatsoever they had a mind. So also the Son of man shall suffer from them. 13 Then the disciples understood, that he had spoken to them of John the Baptist.
There are lots of verses in the OT that speak of a messenger/angel hastily going before to announce the arrival of the Lord and prepare the way. Hence the title pro-dromos/prae-cursor
, even if it doesn't appear as such in Scripture.
Icons of St. John depict him with wings - as an "angel in the flesh", because of his ascetic life, but maybe also to link him with the above mentioned prophecies.