It seems that the psalmist here referred to the Abrahamic covenant. Jehovah promised to bless Abraham’s seed and said that they would take possession of the gate of their enemies.
(‏ مز ١١١ :‏ ٥‏ )‏ يَبْدُو أَنَّ مَنْ نَظَمَ هذَا ٱلْمَزْمُورَ أَشَارَ هُنَا إِلَى ٱلْعَهْدِ ٱلْإِبْرَاهِيمِيِّ .‏