Passage
Hereby shall ye know the Spirit of God, Euery spirit which confesseth that Iesus Christ is come in the flesh, is of God.
1 John 4:2 (GNV)
Nearby Context
1 John 4:1 Dearely beloued, beleeue not euery spirit, but trie the spirits whether they are of God: for many false prophets are gone out into this worlde.
1 John 4:2 Hereby shall ye know the Spirit of God, Euery spirit which confesseth that Iesus Christ is come in the flesh, is of God.
1 John 4:3 And euery spirit that confesseth not that Iesus Christ is come in the flesh, is not of God: but this is the spirit of Antichrist, of whome ye haue heard, how that he should come, and nowe already he is in this world.
1 John 4:4 Litle children, ye are of God, and haue ouercome them: for greater is he that is in you, then he that is in this world.
Study Lenses
The verse centers on "Spirit", "hereby", "shall", "euery", "confesseth", "iesus", and "christ". It is saying that the verse draws attention to "Spirit" and "hereby", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 1's "Dearely beloued beleeue not euery spirit but..." into verse 3's "And euery spirit that confesseth not that...", so "Spirit" and "hereby" belong inside that flow. In 1 John context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "Spirit" and "hereby" with trust shaped by these words, not by a vague optimism outside the passage.