Radak: The matter is repeated in different words. He dug a pit for me to fall in it, and he will fall in it. This was a Nevu'ah that Sha'ul will die via the sword.

Malbim: Keriyah is the beginning of digging. In the parable, the semen of sin was absorbed. Va'Yachperehu (completing the digging) corresponds to pregnancy - he guarded his evil and engaged in it totally, like a woman who guards her fetus at the time of pregnancy. Va'Yipol b'Shachas Yif'al corresponds to birth of Sheker. People who hunt Chayos, they cover a deep pit for the Chayah to fall in it and be destroyed. When he digs the pit to catch people, he himself is caught in it - "Chofer Gumatz Bo Yipol" (Koheles 10:8). The final act (birth) is not like he planned - this is birth of Sheker. Aven is the evil deed done with sin and extortion, without Mishpat. Amel is the bad intent to harm.

Radak: Past tense used in place of future [this is common in Nevu'ah], like I explained (refer to 3:5:2:1).