This is one of those verses we'd all like to apply to those who disagree with us, whose faith we consider impure, for Catholics that would be the Protestants of course, and visa versa. This is exactly what the writer of Titus is doing, writing here specifically of Jewish Christians, those who still hold on to the validity of Mosaic law, and considered unenlightened. No doubt when Titus and co left the room, those Jewish Christians would be saying much the same thing about them: abominable, and disobedient; think they know God but they don't; not like us; etc. etc. It's easy to look at others, and find fault. So rather than trying to find a group of my own to tar with this brush I think I'll use it as a mirror instead.

I profess that I know God; but in works I deny him, being abominable, and disobedient, and unto every good work reprobate. I hope not every good work, and not actually a reprobate, nor abominable and disobedient all of the time, but I admit to such moments, moments with mud in my eyes, or clouds on my heart, making poor decisions, avoiding responsibility, just not stepping up in the way that I'd like to.

I think it is rather a myth that one who truly knows God can never deny Him—just consider those good men with dark secrets; I read about one just yesterday, Trevor Huddleston¹. There are many more. We are humans after all, and each thus flawed. What is beautiful about us, most of us, almost all of us, is that we try. Even after we fail we try again. We reflect, we learn, we improve.² Sometimes we get worse, and then we improve. Life is not static, and we are all on the path to enlightenment, just moving along at different paces to one another. Ultimately though, and for the most part this is an upward spiral.

Fenelon, in one of his own letters³ describes our moments of failure, abominations or disobedience as "pillars of earth", markers that show us how far we have come on our spiritual journey. It's a beautiful reframe, and keeps us from the sin of self-flagellation.

I can claim to know God as I have felt God intervene in my life. This is belief of course, not "fact", but no less meaningful for that. My knowing comes from my experiencing. It doesn't make me God-like, better than others, enlightened, or even faithful. What it did do though was show me a pathway, one that I have been following since.

¹ The line separating good and evil by Jon Kuhrt, Grace+Truth, 24/11/2021
² We improve except where the system/s in which we operate prevent that happening. It the afore-mentioned article the Church of England as an institution failed to hold Huddleston accountable for his misdeeds, thus blocking any opportunity to learn and be redeemed. This sadly is a pattern in many of our institutions today: opacity, lack of responsibility and accountability, basically fear.
³ The Seeking Heart, by François de Salignac de la Mothe-Fénelon, circa 1700