Union and Communion
First, we receive Christ so that we may have him (Ps. 73:25–26), or so that we may be united with him, that he may be in us (Eph. 3:17) and we in him (Eph. 1:13). Communion with Christ Second, we receive Christ so that in and with him we may obtain every kind of saving goods (Rom. 8:32), so that from his fullness we may receive grace upon grace (John 1:12; cf. v. 16), to such a degree that we may be perfect in him (Col. 2:9–10), no different than the way that from the conjugal union flows communion of goods. For this reason it is also said that he who has the Son has life (1 John 5:12).
Petrus van Mastricht. Theoretical-Practical Theology: Faith in the Triune God, ed. Joel R. Beeke, trans. Todd Rester, vol. 2 (Grand Rapids, MI: Reformation Heritage Books, 2019), 48`