The book of Malachi gives us a glimpse of who Jesus is in the Old Testament (O.T).

This is the last book of the Old Testament and it means Messenger. Interesting in this book entitled Messenger, we have two (2) messengers who are explicitly called out. One messenger is with a cause, the other is of the covenant. Malachi 3:1 reads 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. God is silent for the next 300 to years between the Old Testament and the New Testament, and His silence is broken by this messenger.

Messenger #1 is the Messenger with a Cause which was to prepare the way of the Lord (referring to the voice in the wilderness, John the Baptist – Luke 3:4).
And Messenger #2 is the Messenger of the Covenant whom God delights in (referring to Jesus Christ, the Lord). God delights in Jesus. He announced it not once but twice, when he said This is My BELOVED Son, in whom I am well pleased (in whom I delight) at the baptism of Jesus (Luke 3:22) and the transfiguration of Jesus (Matthew 17:5).

In Malachi, Jesus is the Messenger of the covenant, in whom God delights.