a mountain great and high: In Scripture, people often experience God on mountains (compare Ezekiel 40:2; see also Exodus 3:1; 19:10–25; Deuteronomy 34:1–4; 1 Kings 18:20–40; 19:8–18; Matthew 5:1; 15:29; 17:1; 24:3; 28:16).
the holy city … coming down out of heaven from God: People cannot reach God's presence and eternal life by their own efforts. They receive it as a gift (Ephesians 2:8–9; compare 2 Corinthians 5:1).