How does Mark 1:9-20 have a significant impact in Jesus' ministry?
This is a great question. Let me make three points.
First, the baptism scene is essential to the ministry of Jesus. When Jesus was baptized, he entered into his ministry for the first time. From a theological point of view, he began to identify with sinners, as John's baptism was a baptism of repentance. In other words, Jesus is publicly entering into the role of the sin-bearer.
Second, Jesus' time in the wilderness is also important, because he shows that he did not fail like Israel in the wilderness. In other words, the forty years in the wilderness of the Israelites is replicated in Jesus's forty days in the wilderness. The only difference is that Jesus did not fail. He proves that he is the faithful "Israel," the true and perfect son of God.
Third, within these verses, Jesus also choose his inner companions. This is significant, because they will be the ones who carry out his teaching in the future.
From these points of view, we can say that the work of Jesus is adumbrated in these verses.
9-13 shows the way in which God tempts him and tests him despite being his loved son, which means that He is able to 'minister' or speak as a man who has experienced significant hardships and yet still remained faithful.
14-15 is an example of His ministry
16-20 is when He gains his first disciples, which significantly changes the way He talks and the reputation He has; as well as showing the powerful presence He has, and the assistance God gives him, so that men would simply stop work to follow him.