Between Matthew 4 and 19, there is no mention of Judea or the region “beyond the Jordan.” Once He hears of John’s arrest, Jesus withdraws to Galilee (4:12), and doesn’t come back until 19:1.

As soon as He steps back into Judea, the Pharisees come to “test” Him. Apart from 16:1, this word hasn’t been used since chapter 4 either - and then it was used of Satan ( peirazo means “test” or “tempt”). The testing in 16:1 takes place in Galilee, but the instigators are “Pharisees and Sadducees” who “come up,” presumably from Jerusalem.

For Matthew, in short, Judea is the place of testing, the place where Satan assaults Jesus. Jesus returning to Judea is like Moses returning to Egypt after his sojourn in Midian. As soon as Moses tries to cross the boundary to Egypt, the angel of the Lord confronts him; as soon as Jesus arrives in Judea again, the Satanically-inspired Pharisees are there to tempt Him.