Faithful is he that calleth you, who also will do it.
Faithful - to His covenant promises (John 10:27-29; 1 Corinthians 1:9-10; 1 Corinthians 10:13; Philippians 1:6; 2 Timothy 2:13).
He that calleth you. God, the caller of His people, will cause His calling not to fall short of its end.
Do it - preserve and present you blameless at Christ's coming (1 Thessalonians 5:23; Romans 8:30; 1 Peter 5:10). You must not look at the foes before and behind, on the right and the left, but to God's faithfulness to His promises, God's zeal for His honour, and God's love for those whom He calleth.