On temperance and its chief parts, especially tranquillity of mind and moderation, care for what is virtuous, and reflection on what is seemly.
219. As we have spoken of three of the virtues, there remains but the fourth for us to speak of. This is called temperance and moderation; wherein, before all else, tranquillity of mind, the attainment of gentleness, the grace of moderation, regard for what is virtuous, and reflection on what is seemly are sought and looked for.
220. We must keep to a certain order in life, so that a foundation may be laid with our first feelings of modesty, for that is the friend and ally of calmness of mind. Avoiding over-confidence, averse to all excess, it loves sobriety, guards what is honourable, and seeks only what is seemly.
221. Let choice of intercourse come next. Let us link ourselves with older men of approved goodness. For as the companionship of people of our own age is the pleasanter, so that of our elders is the safer. By their guidance and the conduct of their lives they give colour to the character of younger men, and tinge them as it were with the deep purple of probity. For if they who are ignorant of a locality are very glad to take a journey in the company of skilled guides, how much more ought young men to enter on the path of life, which is new to them, in the company of old men; so that they may not go wrong, and turn aside from the true path of virtue. For nothing is better than to have the same men both to direct us in life, and also to be witnesses of how we live.
222. One must also in every action consider what is suitable for different persons, times, and ages, and what will also be in accordance with the abilities of individuals. For often what befits one does not befit another; one thing suits a youth, another an old man; one thing does in danger, another in good fortune.
223. David danced before the ark of the Lord. Samuel did not dance; yet David was not blamed, while the other was praised. David changed his countenance before the king, whose name was Achish. If he had done this without any fear of being recognized, he would certainly not have escaped the charge of levity. Saul also, surrounded by the company of prophets, himself prophesied. Yet of him alone, as though he were unworthy, was it said: “Is Saul also among the prophets?”
Source: On the Duties of the Clergy (New Advent)