Mark quoted scripture "Behold, I send my messenger before thy face, which shall prepare thy way before thee."
- Isa 40:3 ¶ The voice of him that crieth in the wilderness, Prepare ye the way of the LORD, make straight in the desert a highway for our God.
- Isa 57:14 And shall say, Cast ye up, cast ye up, prepare the way, take up the stumblingblock out of the way of my people.
- Mal 3:1 ¶ Behold, I will send my messenger, and he shall prepare the way before me: and the Lord, whom ye seek, shall suddenly come to his temple, even the messenger of the covenant, whom ye delight in: behold, he shall come, saith the LORD of hosts.
The first thing you notice is that Marks quote doesn't look much like a direct quote. Get over it. Standards for quoting, avoiding plagiarism, etc. simply did not exist. Even Jesus paraphrased scripture rather than directly quote it. God's word does not return void. Every translation of scripture is a paraphrase. If you understand scripture, share it. Don't let your inability to quote the English paraphrase word for word stop you.
John is the messenger who prepares the way. He comes before "the Lord", "our God", "my people (Israel)", and "me". Each is a reference to Christ. Mark has identified each prophecy as speaking of Christ. He summarizes them all and addressed them to Christ in "thy face".
Mark had declared Jesus to be the Lord and God. He has equated Israel, which was called the son of God, with the Son of God. And he has Identified him as both the speaker and the subject of the prophecy of Malachi.
The first lesson in hermeneutics is that all scripture speaks of Christ.