'Observe' in the Bible

Only be strong and very courageous, to observe to do according to all the law, which Moses my servant commanded you. Don't turn from it to the right hand or to the left, that you may have good success wherever you go.

This book of the law shall not depart out of your mouth, but you shall meditate on it day and night, that you may observe to do according to all that is written therein: for then you shall make your way prosperous, and then you shall have good success.