1)
Why is it written Magdil, and we pronounce it Migdol?
1.
Radak: It is written like a verb (He increases), and so it says in Tehilim 18:51. We pronounce it [here] like an adjective (a tower). Both mean the same.
2.
Malbim (Tehilim 18:51): Magdil according to the many thanks, so the salvations increase.
2)
To what Chesed does he refer?
1.
Malbim (Tehilim 18:51): 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.
