I will hear what God the Lord will speak. The Church here declares the joy with which she prepares to hear the answer to her prayer in Psalms 85:4. "God the Lord" - literally, 'the God-Yahweh' (cf. Psalms 68:20, "He that is OUR God (literally, the God to us) is the God of salvation").
For he will speak peace unto his people, and to his saints. The Church in faith already anticipates the answer of peace from God. "Peace" spiritually has come "on earth" at Christ's first advent (Luke 2:14). 'Christ died sufficiently for all: efficiently for the elect' (Dr. Davenant, 'De morte Christi'), "His saints." Peace temporally and literally, as well as spiritually, is to come on earth at His second advent, to Israel in their own land, and to all nations (Zechariah 9:10).
But let them not turn again to folly. The redemption of Jesus is designed to "save men from their sins," not that they may continue in their sins (Matthew 1:21; Romans 6:1-2). They who turn again to folly, which all sin is, shall perish in their sinful folly, and "their latter end is worse with them than the beginning;" "the dog is turned to his own vomit again, and the sow that was washed to her wallowing in the mire" (2 Peter 2:20-22). In the case of the spiritual Israel, as well as the literal Israel of the last days, the "everlasting covenant" of God is such as to ensure, as well the complete 'covering' of "all their sin" (Psalms 85:2), as also "that they shall not depart from their God" anymore (Jeremiah 32:38-40; also 31:31-37). God's words, which effect their own command in the case of the elect, "But let them not turn again to folly." (Psalms 80:18) is parallel, the two psalms having a close relation. "So will not we go back from thee: quicken us, and we will call upon thy name."