Answer: The communion in grace which the members of the invisible church have with Christ, is their partaking of the virtue of his mediation, in their justification₁, adoption₂, sanctification, and: Whatever else, in this life, manifests their union with him.₃

1. Romans 8:30
2. Ephesians 1:5
3. 1 Corinthians 1:30

For further study see:

1. Q32: What benefits do they that are effectually called partake of in this life?