he is the true God. See WCF 8.2; WLC 11; HC 35. That Israel's God is the only true and living God is a constant confession throughout Scripture (see notes on Gen 21:33; 1 Sam. 3:7; 17:26; Ps 42:2; 90:2; Jer. 10:10; Isa 43:11-12; Jn. 1:9; 15:1; Acts 4:12; Rev. 3:7). John ends here, defending the full divinity and humanity of Jesus, declaring the Son's intimate relationship with the Father in both his gospel and this letter.
Keep yourselves from idols - 1 John 5:21
idols. See HC 94. The word idols could refer to anything that led people away from the true worship of God (see note on 4:3). However, any congregation in Ephesus or any other city in Asia Minor would have daily experience with physical images of false gods. This would include images of the Roman emperor, who many people worshipped. In the OT, idolatry is a sin that leads to death (see notes on vv. 16-17). Because of the presence of false prophets (see notes on 4:1-6), it is possible that John's command here is quite literal (see notes on Rev. 2:14, 20; 9:20; 13:12, 15)