Isaiah 59:21

In closing, God promised with a covenant promise that He would not withdraw His Spirit or His Word from His people on whom He would place them (cf. Jeremiah 31:31-40). This is a reference to the New Covenant. The Spirit would abide on His people forever, and His Word would remain in their mouths so they could be the witnesses to Him that He created them to be. Since this has not yet happened, it appears that it will happen at the Lord Jesus’ second advent (Isaiah 59:18).

There is debate about whether the Lord has already given His Spirit permanently to all His people, but there is no question that He has not yet made His people the witnesses that they should be. He has given the Spirit to Christians, but not to all Israelites (cf. Joel 2:29). Christians are relatively ineffective witnesses now, but Israel will be a faithful witness in the Millennium (Jeremiah 31:33-34; Ezekiel 36:27 b). Israel will witness to the greatness of Yahweh and will draw the nations to Him (cf. Isaiah 2:2-3; Isaiah 60:1-3). This is the purpose for which He will redeem them.

"The true people of God will ever be a witnessing people, faithfully proclaiming the truth of the Gospel in the power of the Holy Spirit." [Note: Archer, p. 650.]