There is a river - There is no allusion here to any particular stream or river, but the image is designed to represent a state of peace and calm security in contrast with the rough and troubled ocean. While the ocean rages, and foams, and dashes against the mountains as if it would overturn them, the state of Jerusalem, the city of God, was well represented by a calm and gently-flowing river; a river of full banks, diffusing joy and fertility and beauty wherever it flowed. This image, to represent happiness, abundance, peace, joy, is one that is often employed in the Scriptures. Compare Isaiah 32:2; Isaiah 33:21; Isaiah 41:18; Psalms 1:3; Revelation 22:1; Psalms 36:8. The “idea” here is simply that Jerusalem would be calm and serene amidst all the external agitations in the world - calm as a gently-flowing stream. The streams - the canals - the water-courses of such a river flowing around each dwelling and along each garden, would diffuse happiness and beauty everywhere.
The streams whereof - The allusion here is undoubtedly to the canals, watercourses, or rivulets that were led off from the main stream for the purpose of supplying fountains and watering gardens. Thus the city of Damascus is watered by streams or canals cut from the river Barrady, that flows down from the regions of Anti-Libanus. The greenness - the beauty - the fertility - of Damascus is owing wholly to the waters of the river thus conducted to every house and garden in the city. Compare introduction to Isaiah 17:1-14. So here, the flowing river of divine mercy and goodness is conveyed, as in smaller canals or streams, to each home and heart, producing peace, calmness, joy - while the world around is full of commotion and trouble.
Shall make glad the city of God - Jerusalem, considered as the place where God was worshipped, and where he was supposed especially to dwell: Psalms 48:1.
The holy place of the tabernacles of the Most High - Of the “tent” where the Most High is supposed to abide. The word is applicable to any habitation or dwelling-place; but in the Scriptures it is applied especially to the sacred tent erected by Moses in the wilderness, and ultimately removed to Mount Zion by David, as the divine abode on earth. It is sometimes, also, applied to the temple; and if this psalm was written, as I have supposed, in the time of Hezekiah, it would be applicable to that. Compare Psalms 84:2; Psalms 132:5. The tabernacle and the temple were alike divided into two parts - the holy and the most holy place - and hence the “plural” term is sometimes applied to them. Compare the notes at Hebrews 9:2-3.