I’ve heard it said that the New Testament is concealed in the Old Testament and that the OT is revealed in the NT. In the following, I see St. John the Baptist in verse 14, Jesus in verses 15-21, the Holy Spirit mentioned by Jesus in verse 16, and Jesus making a reference to God the Father in verse 21.
14 And it shall be said,
“Build up, build up, prepare the way,
remove every obstruction from my people’s way.”
15 For thus says the high and lofty One
who inhabits eternity, whose name is Holy:
“I dwell in the high and holy place,
and also with him who is of a contrite and humble spirit,
to revive the spirit of the humble,
and to revive the heart of the contrite.
16 For I will not contend for ever,
nor will I always be angry;
for from me proceeds the spirit,
and I have made the breath of life.
17 Because of the iniquity of his covetousness I was angry,
I smote him, I hid my face and was angry;
but he went on backsliding in the way of his own heart.
18 I have seen his ways, but I will heal him;
I will lead him and requite him with comfort,
creating for his mourners the fruit of the lips.
19 Peace, peace, to the far and to the near, says the Lord;
and I will heal him.
20 But the wicked are like the tossing sea;
for it cannot rest,
and its waters toss up mire and dirt.
21 There is no peace, says my God, for the wicked.”