Charles Ellicott Commentary Psalms 89:18

"For our shield belongeth unto Jehovah; And our king to the Holy One of Israel." — Psalms 89:18 (ASV)

For the Lord. —Or, rather—

“For of Jehovah is our shield,
And of Israel’s Holy One our king,”

“shield” and “king” being in synonymous parallelism. Jehovah is the source of the theocratic power.