When Paul lists “self-control” under the fruit of the Spirit, he has a lot more in view than just discipline and impulse control: getting up early and sticking to some dietary goal. The language he uses, literally means “holding in.” Not holding suppression or denial – holding it all in, and refusing all forms of expression, emotional or otherwise. It has a view to expressing some, but not all, in our words, attitudes and actions.
The self-control of the Spirit means you express, but that expression is governed by love and wisdom rather than feeling and whim. We have everyday language for this kind of selective expression. When people lack this, we say someone “needs a filter,” because filters let some things through and hold in others. The water flows through relatively freely, while the coffee grounds are held in place.
We should speak the truth to one another, but you know there is a line where the honesty becomes brutal. So, we should speak the truth but it needs to be self-controlled and filtered by love (Eph 4). This discernment to measure and holding in some and expressing what is loving or helpful is a lot of what the Spirit is giving us in his cultivated fruit of self-control.
“…speaking the truth in love, we are to grow up in every way into him who is the head, into Christ, from whom the whole body, joined and held together by every joint with which it is equipped, when each part is working properly, makes the body grow so that it builds itself up in love.” - Ephesians 4
“…make every effort to supplement your faith with virtue, and virtue with knowledge, and knowledge with self-control, and self-control with steadfastness, and steadfastness with godliness, 7 and godliness with brotherly affection, and brotherly affection with love.” - 2 Peter 1