Charles H. Spurgeon on Psalms 89:51

They have reproached the footsteps of thine anointed. This phrase is obscure in diction, and therefore variously interpreted

1. Some by the footsteps of Christ, judge that his advent in the flesh is meant: others refer the words to David, and take the meaning to be, imitation of him. The first exposition yields this sense: Be mindful, O Lord, of the reproach of thy enemies wherewith they insult our expectation of thy Anointed, and scoff at his advent as if it would never come.

2. The second interpretation is this: Recollect, O Lord, what contempt thy enemies heap upon us on account of thy servant David, because we fondly cherish his memory and his example, and nourish the hope of thy covenant with him, clinging tenaciously thereto...Thirdly, this clause may be so interpreted that by twbqe, that is, the heel, we may understand the extremities of the Kingdom of Christ, of David. Thus we may imagine the enemies of God threw this in the teeth of the people of Israel, that they had already come to the end and extremity of the Kingdom of David. —Musculus.

Verse 51 (second clause). The Chaldee has: "They have scoffed at the tardiness of Thy Messiah's footsteps." So Kimchi: "He delays so long, they say He will never come." Compare 2Pe 3:4,9. The Arabic aqaba is used in the sense of "delaying." —William Kay.