Matthew Poole and continuators on 1 Chronicles 16:35

35 And say ye, Save us, O God of our salvation, and gather us together, and deliver us from the heathen , that we may give thanks to thy holy name, and glory in thy praise.

This might seem an improper and unseasonable Prayer for Davids time when the Israelites were not yet scattered amongst the Heathen, but indeed it was not so: partly because they had already been sadly divided by a Civil War among themselves, and though they were now externally and visibly united under David, yet he might justly think that there were some who yet retained in their Hearts their old Leaven, their hatred of him and their affection to Saul. which might hereafter break forth when Occasion was offered, as it did, 2 Sam. 16. 8. and therefore he justly prays that they may be gathered and united together in hearty Love as well as in outward Shew: and partly because this Psalm or Prayer was made by David for the use of the Church not onely in that present time, but in future Ages, in which David foresaw by the Spirit of Prophecy, or by consideration of those Ancient and Sacred Predictions, Deut. 31. & 32. That the Israelites would one time or other forsake God, and for their Apostacy be dispersed among the Heathens; when they should have great and particular need of this Prayer.