You show them the acts 28 boundary with patience and deliberation using all the evidence you can muster. But after all that - NO! They just will not accept the truth that is glaringly obvious to all who have come to see and appreciate the revelation of "the Mystery".
Some questions require clarification with more questions and answers -- this is one of them. First -- who are we talking to? Is this person saved? If they are not saved then the fact that they don't understand is readily understood since they lack a new nature to understand the things of God.
If saved then they likely have not received the gift of a spirit of wisdom and revelation in the knowledge of Him. Look at what PAul says in Eph. 1:16-18
16 Cease not to give thanks for you, making mention of you in my prayers;
17 That the God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him:
18 The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints,
This is something they may very well lack and if this is so you will not see any progress in this direction until the gift is given and received.
Let us pray that the Father will give this spirit to all who with open heart search and see on this website.