In Verse 16, we have the last reference to Baptism in this chapter.  And something quite spectacular happens.  So let us look at this use of βαπτιζω (5/77).  

Who is being baptized? Jesus was being baptized by John.  
What happened when Jesus was Baptized?  Well as He went up from the water, the heavens were opened.  The Spirit of God descended upon him like a dove, and the Father in Heaven spoke aloud.  
Where did this take place? It was in a public place, not done in secret but in front of others that they might know Jesus is the Son of God. 
Why did God reveal himself here?  It was to announce that Jesus is His Son for the world to know, and to show us the Trinity.  

Now, as we have been asking throughout this chapter, again and again.  Is the Baptism of John from God or from Man? Is it of Heaven above or the earth below.  

My hope is that at this point you can see without a doubt by God's appearing, Baptism is not of man. It is the work of God.