The Galatians were coming to the end of Paul’s letter,

And suddenly the handwriting was different
– instead of the well-formed characters of a professional scribe,
• the printed letters were large and scribbled
◦ this shift was certain to grab their attention
◦ like changing the “font” of a sentence in a document to all upper case or bold print
• but why did Paul insist on writing this last bit with his “own hand”?
◦ perhaps this is how he usually signed off (as many commentaries point out)
“I, Paul, write this greeting with my own hand. This is the sign of genuineness in every letter of mine; it is the way I write” (2 Thes. 3:17 )
◦ or, he wanted to ensure that they took notice, and that is why he drew attention to it