Charles H. Spurgeon on Psalms 89:15

Blessed is the people that know the joyful sound. It is a blessed God of whom the Psalmist has been singing, and therefore they are a blessed people who partake of his bounty, and know how to exult in his favour. Praise is a peculiarly joyful sound, and blessed are those who are familiar with its strains. The covenant promises have also a sound beyond measure precious, and they are highly favoured who understand their meaning and recognise their own personal interest in them. There may also be a reference here to the blowing of trumpets and other glad noises which attended the worship of Jehovah, who, unlike the gods of the heathen was not adored by the shrieks of wretched victims, or the yells and outcries of terror stricken crowds, but by the joyful shouts of his happy people. They shall walk, O LORD, in the light of thy countenance. For them it is joy enough that Jehovah is favourable to them; all day long this contents them and enables them with rigour to pursue their pilgrimage. Only a covenant God could look with favour upon men, and those who have known him in that relationship learn to rejoice in him, yea, to walk with him in fellowship, and to continue in communion with him. If we give God our ear and hear the joyful sound, he will shew us his face and make us glad. While the sun shines, men walk without stumbling as to their feet, and when the Lord smiles on us we live without grief as to our souls.