If anyone attacks the security of the believer, first of all he is attacking God and claiming He changed His verdict. Second, he is attacking Christ and claiming His work on the cross was inadequate and that His high-priestly work can’t maintain us. Finally, he is attacking the Holy Spirit and claiming He is inadequate to help the believer persevere. A discrediting of the Trinity is wrapped up in a denial of the security of salvation.
John McArthur
Website: https://www.gty.org/library/study-guides/180/eternal-security