"Let all discords and enmities be laid aside, and let no one think to have a share in the Paschal feast that has neglected to restore brotherly peace," he said in another.
Care for the poor and others in need should be an even greater priority.
"Let us not pass over the groans of the poor with deaf ear, but with prompt kindness bestow our mercy on the needy, that we may deserve to find mercy in the judgment," said the saint, later adding "let each bestow on the weak and destitute those dainties which he denies himself."
"Let our humaneness be felt by the sick in their illnesses, by the weakly in their infirmities, by the exiles in their hardships, by the orphans in their destitution, and by solitary widows in their sadness: in the helping of whom there is no one that cannot carry out some amount of benevolence," he continued.
Warning against the dangers of spiritual pride and hypocrisy, he also gave advice on how to follow Lenten disciplines.
"The self-restraint of the religious should not be gloomy, but sincere; no murmurs of complaint should be heard from those who are never without the consolation of holy joys," he said, adding "no one is so holy that he ought not to be holier, nor so devout that he might not be devouter."
At times, the foes of Christians are not simply the flesh, but even the demonic, he said. The approach of Easter makes the devil grow "furious" and "consumed with the strongest jealousy and now tortured with the greatest vexation."
It is a time when "the Christian army has to combat him, and any that have grown lukewarm and slothful, or that are absorbed in worldly cares, must now be furnished with spiritual armor and their ardor kindled for the fray by the heavenly trumpet."
The approaching baptism of new Christians at Easter, and the growing penitence of lapsed Christians, is also a target of the devil's anger.
"For he sees whole tribes of the human race brought in afresh to the adoption of God's sons and the offspring of the New Birth multiplied through the virgin fertility of the Church," St. Leo the Great said. "He sees himself robbed of all his tyrannical power, and driven from the hearts of those he once possessed, while from either sex, thousands of the old, the young, the middle-aged are snatched away from him, and no one is debarred by sin either of his own or original."
The devil sees, too, those who have lapsed, "deceived by his treacherous snares," now becoming "washed in the tears of penitence" and seeking mercy and reconciliation in the Church.
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Leo the Great also promoted fasting as a way to prepare to conquer earthly foes.
When the Hebrews and Israelites were oppressed by the Philistines "for their scandalous sins," they restored their mental and physical powers by commanding a fast in order to be able to overcome their enemies.
"For they understood that they had deserved that hard and wretched subjection for their neglect of God's commands, and evil ways, and that it was in vain for them to strive with arms unless they had first withstood their sin," he said.
Abstinence from food and drink was "the discipline of strict correction," he said. In order to defeat their foes, they "first conquered the allurements of the palate in themselves."
Similarly, those of us who face opposition and conflict "may be cured by a little carefulness, if only we will use the same means."
Though all seasons of the year are full of God's blessings, St. Leo the Great said, Lent is a time when "all men's minds should be moved with greater zeal to spiritual progress." Lenten discipline "should heal us and restore the purity of our minds, during which the faults of other times might be redeemed by pious acts and removed by chaste fasting."