Adam Clarke on Deuteronomy 30:20

That thou mayest love the Lord - Without love there can be no obedience.

Obey his voice - Without obedience love is fruitless and dead.

And cleave unto him - Without close attachment and perseverance, temporary love, however sincere and fervent - temporary obedience, however disinterested, energetic, and pure while it lasts - will be ultimately ineffectual. He alone who endures to the end, shall be saved. Reader, how do matters stand between God and thy soul? He cannot persevere in the grace of God whose soul is not yet made a partaker of that grace. Many talk strenuously on the impossibility of falling from grace, who have not yet tasted that the Lord is gracious. How absurd to talk and dispute about the infallibility of arriving safely at the end of a way in which a man has never yet taken one hearty step! It is never among those that have the grace of God, but among those that have it not, that we find an overweening confidence.