Revelation 2:4-5 Nevertheless I have somewhat against thee, because thou hast left thy first love.Remember therefore from whence thou art fallen, and repent, and do the first works; or else I will come unto thee quickly, and will remove thy candlestick out of his place, except thou repent.

In the early church at Jerusalem, when Pentecost came, the Spirit of God came mightily to save many and a description of that first love is given to us in Acts 2:41-47.

Acts 2:41 Then they that gladly received his word were baptized: and the same day there were added unto themabout three thousand souls. 42 And they continued stedfastly in the apostles’ doctrine and fellowship, and in breaking of bread, and in prayers. 43 And fear came upon every soul: and many wonders and signs were done by the apostles. 44 And all that believed were together, and had all things common; 45 And sold their possessions and goods, and parted them to all men, as every man had need. 46 And they, continuing daily with one accord in the temple, and breaking bread from house to house, did eat their meat with gladness and singleness of heart, 47 Praising God, and having favour with all the people. And the Lord added to the church daily such as should be saved.

This is the church that is living in her first love. Brotherly love was an authentic proof of faith in Christ. They shared their resources. Brotherly love cannot be separated or substituted from love for Christ, but it is a proof of that love.