The writer of Psalm 83:18 professes that Jehovah/YHWH is the Most High God (EL ELYON) and the Most High himself made another emphatic declaration over 2000 years ago: "You are my witnesses" (Isaiah 43:10-12). But fleshly Israel did not render Jehovah implicit obedience. As a result, the nation lost its unique privilege to exalt God's majesty (Exodus 19:5, 6). The Christian congregation is now a "people for God's name" (Acts 15:14). It is this congregation that not only witnesses about Christ, but also testifies with respect to the God and Father of Christ Jesus.
Please see Revelation 1:9 which informs us why John was placed in prison. Not only was he incarcerated because he bore witness to Christ, but he also was bound "for the word of God." John was persecuted for magnifying the Most High--the God and Father of Jesus Christ.
"and the power of the Highest shall overshadow thee (καὶ δύναμις Ὑψίστου ἐπισκιάσει σοι)"-Luke 1:35
Compare Luke 1:32, 76; 6:35; 8:28.