5 if only you fully obey the LORD your God and are careful to follow all these commands I am giving you today.

Read Deuteronomy 15:5 Using Other Translations

Only if thou carefully hearken unto the voice of the LORD thy God, to observe to do all these commandments which I command thee this day.
if only you will strictly obey the voice of the LORD your God, being careful to do all this commandment that I command you today.
You will receive this blessing if you are careful to obey all the commands of the LORD your God that I am giving you today.