We know we are in the faith through self-examination, the preaching of the gospel, and the presence of love for Christ and others.
The assurance of being in the faith comes from multiple sources. First, self-examination as encouraged in 2 Corinthians 13:5 allows the believer to reflect deeply on their relationship with Christ. Secondly, being in the faith means engaging with the gospel as presented through preaching, where Christ is central. Furthermore, a genuine love for one's brethren is a sign of being in the faith, as love is a natural outflow of being in Christ. As 1 John 2:3 indicates, keeping the commandments of Christ and showing love for others are evidences of knowing Him. Thus, the faithful believer can rejoice in the assurance that they are in the faith through these markers.
Scripture References:
2 Corinthians 13:5, 1 John 2:3, John 14:20, 1 John 2:19, Jeremiah 32:40, Jude 1:3, Philippians 1:27
Commentary