Sincerity lies at the root of all gracious profession. If a man be not sincere he is nothing. God makes a man sincere by planting his truth in his heart; and whenever God does make a man sincere, the truth which he has implanted will grow. Truth does not lie in a man's soul dead and motionless, like a stone in the street; it is a living, active, expansive principle.
If the truth be in the soul it will be ever pushing out error, because the two principles cannot exist together; and as Isaac thrust out Ishmael, and Jacob proved stronger than Esau, so will simplicity and godly sincerity be ever mightier than craft and deception. The truth of God in the heart will not wither and die, but will be shined upon by the Sun of righteousness, and sunned into fruitfulness by the smiles of God; and as truth becomes day by day more and more precious, so will error and evil become day by day more and more hateful. A sincere soul stands "girt about with truth;" and truth forms its shield and buckler.
But how does this Christian sincerity prove the soul's safeguard from error? By putting it ever on the watch tower, looking out and looking up for the teaching of God and the light of his countenance. A soul made spiritually sincere takes nothing upon trust; it requires the seal of God on all it receives, and the witness of the Spirit to all that it feels. He who is sincere sees the rocks ahead on which others concerning faith make shipwreck; and being well ballasted with temptations, afflictions, and trials, he is not easily tossed to and fro with every wind of doctrine. His desire to be right keeps him right; his fear to be wrong preserves him from wrong. The light of God in his soul makes him see; the life of God in his heart makes him feel; the fear of God in his conscience makes him honest; the love of God in his affections makes him love; and all this gives truth such a firm place in him that there is no room for error.
The Apostle adds, therefore, "in love." It is not enough to be "sincere;" we must be "sincere in love." Mark that. It is not receiving God's truth as a certain orderly system; it is not furnishing our heads with a sound doctrinal creed and compact Calvinistic scheme which will avail us in the trying hour; but it is to have the truth of God brought into our soul by a divine power, and realising such unutterable sweetness in it as communicates a firm abiding love, both to the truth itself, and to Him of whom it testifies and from whom it comes.
It is thus we are made "sincere in love." The fear of God creates the sincerity, the application of the truth with power creates the love to it. And when we are thus made "sincere in love" we are brought out of the childish state in which we are carried about with every wind of doctrine, and in danger of being entrapped by the cunning craft of every deceiver. We know the truth, love the truth, and become established in the truth.