For the honor of thy servant - i. e., “for the honor which Thou hast done for Thy servant.” The Septuagint omits “Thy servant,” and renders it: “What can David say more to Thee to glorify Thee? For Thou knowest,” etc.
SDA Bible Commentary (limited)
Volume 1-7
18. Speak more. What could David say more to glorify God, in view of the unparalleled honor God had shown to His servant? David was overwhelmed by the high honor God had shown to him, and words failed him to express the feelings of gratefulness that welled up within his heart.