Dora Bas Rivka Silver O'H
In the future, the king will rejoice in G-d's might. ("The king" may refer to Moshiach, the Messiah. The word "yismach" - "will rejoice" - is an anagram of Moshiach.) How much does he praise G-d for His salvation! G-d has granted his desires and requests. He has blessed him with goodness and placed a golden crown on his head.
David asked G-d for life and G-d granted it, as well as an everlasting dynasty. Plus, He allowed David to overcome his enemies and gave him honor. He made David the subject of a blessing (as He did with Abraham) and He will be with David's descendant, Moshiach, in future times. G-d has infinite power to grant such kindnesses.
G-d will pinpoint His enemies and consume them in His anger. David prays that G-d will put an end to their descendants, possibly referring to the nation of Amalek. These enemies plot against G-d, but such schemes are doomed to fail. Such people are totally removed from G-d, so He points His metaphorical weapon at them. May G-d be exalted and we praise His might.