66:1-4 The psalmist speaking for his nation called the other nations to join in praise by shouting, singing, and speaking. In verses 1-12 he wrote in the first person plural, but in verses 13-20 he used the first person singular. God's great acts made His enemies cringe before Him. "Feigned obedience"(v. 3, NASB) is hypocritical obedience. The psalmist meant God's enemies would pretend to obey Him because they feared His wrath if they did not really obey Him.
66:5-7 God's great acts in nature and history demonstrate His sovereign authority over all the earth. The Red Sea and Jordan River crossings demonstrated this authority to all the nations (cf. Josh. 2:9-11). Nations should therefore pause before rebelling against the Lord.
66:8-9 Again the psalmist called the nations to bless God because of what He had done in preserving Israel.
66:10-12 God had also disciplined Israel to bring out the best in her. He had put her through trials of fire and trials of water, the two prominent testing media. Through all her testings God had not abandoned His people but had brought them through to greater blessing.