Charles Ellicott Commentary 1 Chronicles 22:13

"Then shalt thou prosper, if thou observe to do the statutes and the ordinances which Jehovah charged Moses with concerning Israel: be strong, and of good courage; fear not, neither be dismayed." — 1 Chronicles 22:13 (ASV)

Then you shall prosper. — The verse makes it quite clear that obedience was an indispensable condition for the full realization of the promise. (Compare 1 Chronicles 22:10 with the actual subsequent course of history.) Yet the word of the Lord does not return to Him void; and if the earthly dynasty of David came to an end through disobedience, in due time an heir of David and Solomon was born, who is today the Lord of a spiritual dominion which will endure throughout the ages.

If you take heed to fulfill. — Literally, if you keep to do the statutes and judgments: language which is obviously reminiscent of Deuteronomy. (Deuteronomy 11:32.)

Be strong, and of good courage. — Or, Be strong and staunch! a frequent phrase in Joshua (1 Chronicles 1:7, and other verses).

Dread not, nor be dismayed. — So Deuteronomy 1:21; Deuteronomy 31:8; Joshua 1:9.

Dismayed. — Broken, i.e., in spirit: metu fractus. (Compare “Solomon my son is young and timid,” 1 Chronicles 22:5.)