“For which reason I testify to you this day, that I am pure from the blood of all men. For I shrank not from declaring to you the whole counsel (or ‘will') of God.”
And this is why he wants them to know that he has fully discharged his responsibility. That he is pure from the blood of all men. That he has done all that he could. That no charge of unfaithfulness can be laid at his door. Because at no stage has he shrunk from, or failed in his responsibility to, the declaration to them of every aspect of God's purposes, and way, and will, and being. He has shown them all that God has provided for them and requires of them. He has left nothing out.
No doubt it was important to Paul that all recognised that he had done his duty. But it is also a call to them to consider the words of Ezekiel 33:8 and be the same as he was. He has given an example that they might follow in his steps as he follows Christ (1 Corinthians 11:1).
He Warns Them to Watch Over The Church Faithfully Because of False Teachers Who Will Come Among Them and Rise Up Among Them, So That They Must Constantly Be On The Watch In Order To Combat Them (Acts 20:28-31).
As the central point in the chiasmus we now come to the idea to which all the remainder is pointing, the dangers that lie ahead for the church as a result of false teachers. He has good cause to recognise this danger. It is this kind of thing that above all has caused his tears. As he looks back to what had already happened to the churches in Galatia (Galatians 4:11; Galatians 4:19) and Corinth (2 Corinthians 2:4) and Syrian Antioch, he knows that at some point Ephesus must face it too. For Satan is ever active. He has seen it too often before not to be aware that it will come. And he wants them to be ready for it. It is no accident that in the larger chiasmus from Acts 19:21 to Acts 28:31 (see above) this parallels the almost unbelievable storm described in Acts 27:14-44 which illustrates so vividly what the effects of false words can be in seeking to sweep away the souls of men, and what we must be willing to sacrifice in order to come through unscathed. There men were ready to betray those who trusted in them. And it was only because men listened to Paul's words that they were prevented. Luke is letting us all know that if we are to come through the storms of life safely we must cling to nothing other than God, but must willingly let all go, so that we may go forward with our whole trust in God and His word alone.