And thou shalt love the LORD thy God with all thine heart, and with all thy soul, and with all thy might. – Deuteronomy 6:5

The first duty of a Christian man is to obey God. Obedience is hard work to proud flesh and blood; indeed, these ingrained rebels will never obey through our own efforts. By nature we love our own will and way; and it goes against the grain for us to bring ourselves into such complete subjection as the law of the Lord requires. “Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.” Who among us has done this? Who among us can do this, unless a power outside of himself shall come to his aid? Faith alone takes hold of the divine strength; and only by that strength can we obey. Hence faith is the essential point of holiness. Ah, my dear friend! if you start on the voyage of life, by divine grace, with the resolve that you will follow the track; marked down on the chart by the Lord your God, you will find that you have chosen a course to which the Lord’s hand alone can keep you true. The current does not run that way. Before long you will find that the wind is dead against you, and the course to be followed is hard to keep. What will you do then if you have not faith? When duty is contrary to your temperament, what will you do without faith? When it involves loss of money, or ease, or honor, what will you do then if you have no faith? If you believe that God is the Rewarder of them that diligently seek Him, you will persevere; but not else. Suppose the right course should expose you to ridicule, cause you to be spoken of as a fanatic, or mocked at as a hypocrite, or despised as a fool, what can you do without faith? If you trust the living God, you will do the right, and bear the loss or the shame; but if your faith fail you, self-love will create such respect for your own good name, such fear of ridicule, such unwillingness to be singular, that you will slide from your integrity, and choose a smooth and pleasing road. Though you may think it a very ordinary thing to obey God in all things, you will find that a man had need to set his face like a flint in order to keep the right road; and the only way in which he will be able to hold on his way will be by having faith in God. Let him say, “God commands, and therefore I must do it;” and he will be strong. Let him say, “God commands, and therefore he will bear me through;” and he will be strong. Let him say, “God commands, and he will recompense me,” and he will be strong. We are not saved by obedience, for obedience is the result of salvation. We are saved by faith, because faith leads us to obey. Faith is weakness clinging to strength, and becoming strong through so doing. Faith in God made the cripple at the temple gate stand, and walk, and leap, and praise God; and even so does faith make our sin-crippled manhood obey the will of the Lord with exultation. – C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2209.cfm