The antecedent of "it" ( Psalm 132:6) is the ark ( Psalm 132:8). Ephrathah (Ephratah) is an old name for the area around Bethlehem ( Genesis 35:16; Genesis 35:19; Genesis 48:7). Jaar evidently refers to Kiriath-jearim, "Jearim" being the plural of "Jaar," the town where the ark rested for20 years after the Philistines returned it ( 1 Samuel 7:1-2). Evidently some Israelites in Bethlehem heard that the ark was in Kiriath-jearim and went there to retrieve it. From there, David then brought the ark into Jerusalem ( 2 Samuel 6). [1][source]
The Israelite pilgrims who sang this psalm resolved to go to worship God on Mt. Zion, to the place in Jerusalem where the ark rested ( Psalm 132:7), referred to here as God"s "footstool." That was where God dwelt in a localized way among His people. It was His earthly throne. They called on God to meet with them there. They spoke of "the ark of God"s strength" because it represented God"s strength in Israel"s previous battles. [source][source][source]