Jesus, the Lamb of God, God’s Chosen One

John 1:29-34

29 The next day John saw Jesus coming towards him and said, ‘Look, the Lamb of God, who takes away the sin of the world! 30 This is the one I meant when I said, “A man who comes after me has surpassed me because he was before me.” 31 I myself did not know him, but the reason I came baptising with water was that he might be revealed to Israel.’
32 Then John gave this testimony: ‘I saw the Spirit come down from heaven as a dove and remain on him. 33 And I myself did not know him, but the one who sent me to baptise with water told me, “The man on whom you see the Spirit come down and remain is the one who will baptise with the Holy Spirit.” 34 I have seen and I testify that this is God’s Chosen One.’

I. John’s Testimony: Jesus is the Lamb of God (29-31)

When John the Baptist saw Jesus, he testified

“Look, the Lamb of God, who takes away the sin of the world!” (29)

Why is Jesus called ‘the Lamb of God’? ‘The Lamb’ represents ‘the Passover lamb’ (Exodus 12:21) sacrificed during the ‘Passover’ event written in Exodus 12:1-30. The Israelites put the blood of the lamb on the sides and tops of door-frames of the houses (Exodus 12:6-7, Exodus 12:21-22) and when God saw the blood, he ‘passed over’ them without striking them with the destructive plague (Exodus 12:12-13, Exodus 12:23).

In the Law, God let us forgiven by sacrificing an animal(s) (e.g., bull, sheep) without defect (e.g., Leviticus 4, 5, 7, 14).

Jesus (the Lamb of God) who was without sin (without defect) died for us to take our sin away! Because he received the punishment we deserve (Isaiah 53), we are forgiven when we believe him (Romans 10:9-13). He did this because he loves us. This is the good news of salvation for all humanity.

“A man who comes after me has surpassed me because he was before me.” (30) was mentioned in John 1:15.

‘John testified concerning him. He cried out, saying, “This is the one I spoke about when I said, “He who comes after me has surpassed me because he was before me.” ’ (John 1:15)

This John is Baptist (= Baptiser or Witness) John. He was an excellent prophet like Elijah. So, people could think he might be the Messiah. But, he was not the light, but a witness to the light (John 1:8), expressing himself as ‘the voice’ (John 1:23). John made it clear “Jesus is greater” which reason John told was that Jesus was ‘before’ him, even though he was born 6 months earlier than Jesus on the earth. We learn that it is important to know and testify the fact that the Word existed before the creation as written in John 1:1-14.

This is called the pre-existence of Christ. That is, Jesus was a pre-existent divine hypostasis (=the underlying state or underlying substance and is the fundamental reality that supports all else [3]) [2].

Regarding minimum preparation for witnessing as a believer, one may refer to 1 Peter 3:15. As a disciple, one may refer to Matthew 28:18-20.

See John 1:31.

I myself did not know him, but the reason I came baptising with water was that he might be revealed to Israel.’

The object of John's baptism [4] includes

1. "Preparing a people for the Lord" (Isaiah 40:3-5, Luke 3:4-6).
2. "The Messiah might be revealed to Israel" (John 1:31).

Jesus was revealed as Messiah during the baptism in John 1:32-34.

See John 1:32-34

32 Then John gave this testimony: ‘I saw the Spirit come down from heaven as a dove and remain on him. 33 And I myself did not know him, but the one who sent me to baptise with water told me, “The man on whom you see the Spirit come down and remain is the one who will baptise with the Holy Spirit.” 34 I have seen and I testify that this is God’s Chosen One.’

John the Baptist was kinsman of Jesus and born 6 months before Jesus. But John says "I myself did not know him" in John 1:31 and again John 1:33.

John’s 'knowledge' here was obtained via God’s revelation, which John heard (33) and saw (32, 34).

Some knowledge is given by God's will & selection (Matthew 11:27).

... no one knows the Father except the Son and those to whom the Son chooses to reveal him.

When Peter said to Jesus, ‘You are the Messiah, the Son of the living God.’ in Matthew 16:16, Jesus said that this was revealed to Peter by His Father in heaven. See Matthew 16:17.

‘Blessed are you, Simon son of Jonah, for this was not revealed to you by flesh and blood, but by my Father in heaven.’

We can see a similar principle in John 1:12-13.

12 Yet to all who did receive him, to those who believed in his name, he gave the right to become children of God—13 children born not of natural descent, nor of human decision or a husband’s will, but born of God.

• natural descent (13a): physical birth [5]
• human decision (13b): self-determination [5]
• a husband’s will (13c): the choice of another person [5]

Finally, see John 1:34.

I have seen and I testify that this is God’s Chosen One.’

Here, ‘I have seen’ means that John saw “the Spirit come down and remain on Jesus” (32, 33).
The term “God’s Chosen One”, that indicates the Messiah, is written in Isaiah 42:1

‘Here is my servant, whom I uphold,
my chosen one in whom I delight;
I will put my Spirit on him,
and he will bring justice to the nations.

References
[1] The Holy Bible: New International Version (Anglicised Edition, 2011), Revised and updated edition. (London: Hodder & Stoughton, 2011).
[2] Wikipedia. Pre-existence of Christ.
[3] Wikipedia. hypostasis.
[4] John Peter Lange and Philip Schaff, A Commentary on the Holy Scriptures: John (Bellingham, WA: Logos Bible Software, 2008), 87.
[5] Gangel, K. O. (2000). John (Vol. 4, p. 12). Nashville, TN: Broadman & Holman Publishers.