1)
Why does it say here Magdil, and in Shmuel II (22:51) we pronounce it Migdol?
1.
Radak: Magdil is a verb (He increases). In Shmuel, we pronounce it like an adjective (a tower). Both mean the same.
2.
Malbim: Magdil - according to the many thanks, so the salvations increase.
2)
To what Chesed does he refer?
1.
Malbim: Apart from rewarding me for the thanks and praise, He does Chesed to his Mashi'ach, to David. He made a Bris that kingship will never cease from his seed.
