For Augustine in City of God 21.16, your best life now consists in waging war against the flesh as long as you live. But the power to fight this war comes only from God, and is accessed only through faith:
And indeed this victory cannot be sincerely and truly gained but by delighting in true righteousness, and it is faith in Christ that gives this.
Though outward, external, and obvious vices can sometimes be overcome, to man’s eyes, by other hidden vices, such as pride, true victory comes from true virtue, which springs from the love of God that makes him an object of more delight than our own wickedness: and this can only be found through the work of the Mediator, the God-Man Jesus Christ, present by the power of his Spirit:
Accordingly vices are then only to be considered overcome when they are conquered by the love of God, which God Himself alone gives, and which He gives only through the Mediator between God and men, the man Christ Jesus, who became a partaker of our mortality that He might make us partakers of His divinity.
Otherwise, if the Spirit were to be absent, the law would only increase our transgression:
For if the law be present with its command, and the Spirit be absent with His help, the presence of the prohibition serves only to increase the desire to sin, and adds the guilt of transgression.
What does this look like? It looks like grace, grace that triumphs over our parodic self-sufficiency. It is only grace working in us that yields repentance and the love of God:
The greater number having first become transgressors of the law that they have received, and having allowed vice to have the ascendency in them, then flee to grace for help, and so, by a penitence more bitter, and a struggle more violent than it would otherwise have been, they subdue the soul to God, and thus give it its lawful authority over the flesh, and become victors.
This war must be waged now, for after death it will be too late. The only postmortem pains to be discovered are those of the Last Judgment. We must not only be baptized, then; we must also find our righteousness in Christ, now–or never. 1
Whoever, therefore, desires to escape eternal punishment, let him not only be baptized, but also justified in Christ, and so let him in truth pass from the devil to Christ. And let him not fancy that there are any purgatorial pains except before that final and dreadful judgment.
So what does your best life now look like? War against the flesh, through the help of God by his grace in Christ. But this work of “subduing the soul to God” is rooted in God’s prior action. So be of good cheer: if he has called you, and you have called upon him, he has already called you a saint–and we know that God’s word never returns to him void, but accomplishes what he has sent it forth to do. So you are; and now we must, with Paul, put on the full armor of God. Our war is waged in the hope that the Lord will surely fulfill his promises. Yet a little while, and the God of peace will crush Satan under our feet.