An excellent word for Christian apologists—and all of us—from the Prince of Puritans, John Owen:
That direction, in this kind, which with me is instar omnium [equivalent to all], is for a diligent endeavor to have the power of the truths professed and contended for abiding upon our hearts, that we may not contend for notions, but that we have a practical acquaintance with in our own souls. When the heart is cast indeed into the mould of the doctrine that the mind embraceth; when the evidence and necessity of the truth abides in us; when not the sense of the words only is in our heads, but the sense of the things abides in our hearts; when we have communion with God in the doctrine we contend for, — then shall we be garrisoned, by the grace of God, against all the assaults of men. And without this all our contending is, as to ourselves, of no value. What am I the better if I can dispute that Christ is God, but have no sense or sweetness in my heart from hence that he is a God in covenant with my soul? What will it avail me to evince, by testimonies and arguments, that he hath made satisfaction for sin, if, through my unbelief, the wrath of God abideth on me, and I have no experience of my own being made the righteousness of God in him, — if I find not, in my standing before God, the excellency of having my sins imputed to him and his righteousness imputed to me? Will it be any advantage to me, in the issue, to profess and dispute that God works the conversion of a sinner by the irresistible grace of his Spirit, if I was never acquainted experimentally with the deadness and utter impotency to good, that opposition to the law of God, which is in my own soul by nature, with the efficacy of the exceeding greatness of the power of God in quickening, enlightening, and bringing forth the fruits of obedience in me? It is the power of truth in the heart alone that will make us cleave unto it indeed in an hour of temptation. Let us, then, not think that we are any thing the better for our conviction of the truths of the great doctrines of the gospel, for which we contend with these men, unless we find the power of the truths abiding in our own hearts, and have a continual experience of their necessity and excellency in our standing before God and our communion with him.
(The Works of John Owen, vol. 12, p. 52)