Joel 2:32 And it shall come to pass, that whosoever shall call on the name of the LORD (Hebrew = IEUE or YHWH) shall be delivered: for in mount Zion and in Jerusalem shall be deliverance, as the LORD (Hebrew = IEUE or YHWH) hath said, and in the remnant whom the LORD shall call.
Rom 10:13 For whosoever shall call upon the name of the Lord shall be saved.
Paul is a directly quoting from Joel 2:32.
Isa 45:21 Tell ye, and bring them near; yea, let them take counsel together: who hath declared this from ancient time? who hath told it from that time? have not I the LORD? (Hebrew = IEUE or YWYH) and there is no God else beside me; a just God (Hebrew = EL) and a Saviour; there is none beside me.
Isa 45:22 Look unto me, and be ye saved, all the ends of the earth: for I am God, and there is none else.
Isa 45:23 I have sworn by myself, the word is gone out of my mouth in righteousness, and shall not return, That unto me every knee shall bow, every tongue shall swear.
Paul:
Phil 2:10 That at the name of Jesus every knee should bow, of things in heaven, and things in earth, and things under the earth;
Phil 2:11 And that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father.
So here again Paul is equating or stating Jesus is the incarnate God of Israel YHWH.
---------------------------------------------
(Isa 41:4 Who hath wrought and done it, calling the generations from the beginning? I the LORD (YWYH), the first, and with the last; I am he.
Isa 44:6 Thus saith the LORD the King of Israel, and his redeemer the LORD of hosts; I am the first, and I am the last; and beside me there is no God.
Isa 48:12 Hearken unto me, O Jacob and Israel, my called; I am he; I am the first, I also am the last.
In the Book of Revelation - more correctly called "The Unveiling of Jesus Christ" the Lord Jesus is "revealing" himself as YHWH of the "old testament" to John and his readers:
Rev 1:11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches...
Rev 1:17 And when I saw him, I fell at his feet as dead. And he laid his right hand upon me, saying unto me, Fear not; I am the first and the last:
Rev 1:18 I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death.
----------------------------------------
John the Baptist is applying the prophecy of Isaiah to proclaim that Jesus is the Lord spoken of in that verse:
(Mat 3:3 KJV) For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight.
(Isa 40:3 KJV) The voice of him that crieth in the wilderness, Prepare ye the way of the LORD (Hebrew = IEUE YHYH), make straight in the desert a highway for our God.
There can be no more clearer indication from the above that the early Christians understood that Jesus was YHWH "the first and last" of the old testament.