Gods rest, or heaven, is available to us, but the author of Hebrews warns us that a lack of faith, similar to what the Israelites displayed, will prevent us from ever entering Gods rest. Therefore, all that Christ has done for us as a High Priest will be in vain. 

Scripture References: 

Hebrews 4:14–16 (NLT)
2 Thessalonians 2:13–15 (NLT)
Deuteronomy 11:8–9 (NLT)
1 John 3:21–22 (NLT)
Colossians 1:19–23 (NLT)