John Wesley on Deuteronomy 30:20

That thou mayest love the Lord thy God - Here he shews them in short, what their duty is; To love God as the Lord, a being most amiable, and as their God, a God in covenant with them: as an evidence of their love, to obey his voice in every thing, and by constancy in this love and obedience, to cleave to him all their days. And what encouragement had they to do this? For he is thy life and the length of thy days - He gives life, preserves life, restores life, and prolongs it, by his power, tho' it be a frail life, and by his presence, tho' it be a forfeited life. He sweetens life by his comforts, and compleats all in life everlasting.