God. See App-98., with Art. Contrast John 1:1.
a Spirit. spirit: i.e. not flesh, or material substance. Not "a" Spirit.
must. Note this absolute condition. Compare John 4:4; John 3:7; John 3:14; John 3:30; John 9:4; John 10:16; John 12:34; John 20:9, &c.