What does Psalm 66:8 mean?

Again (Psalm 66:1), the psalmist calls upon the entire world of mankind to acclaim the Lord. Israel's very existence was meant to provide clear evidence that God is good and almighty (Deuteronomy 14:2). The Gentiles could not deny that God cared for His people. At times, He defended them with awesome power (Isaiah 37:36; Exodus 14:21–22). Even when Israel was humbled, it was under God's control and for His purposes (2 Kings 18:11–12).

Today, both Jews and Gentiles who believe on Jesus as Savior have overwhelming evidence of His goodness, and this evidence leads them to bless God. In Ephesians, the apostle Paul reminds Ephesian Christians that God has provided encouragement through Christ (Ephesians 1:3). Believers should praise the Lord God because He chose them, made them holy (Ephesians 1:4), predestined them to become His children (Ephesians 1:5), redeemed them through Jesus' blood (Ephesians 1:7), forgave them (Ephesians 1:7), poured incredible grace and wisdom on them (Ephesians 1:8), and allowed a glimpse into the mystery of His will (Ephesians 1:9).