“And God has given us his Spirit as proof that we live in him and he in us” (1 John 4:13 NLT)

What the apostle John here calls “proof,” the apostle Paul calls a “guarantee (deposit, earnest, pledge)” (Eph. 1:14). Paul spoke of how the Holy Spirit seals our salvation, giving us inward assurance of salvation. But John is more concerned with what this mutual abiding looks like outwardly. He says that the one who lives in the Spirit and has the Spirit living in him, will testify that Jesus is the Son of God with his lips and have the love of God for others in his actions. The outworking of the Spirit living in us is evidenced by our testimony about Jesus and our love of others.