If so be that ye have heard him; either heard Christ speaking to you in the gospel, Heb_12:25, and then the sense will be the same as in the following clause; or heard him preached to you, and then it may refer to the outward hearing of the word.
And have been taught by him; or taught in him; in or by, as Col_1:16Heb_1:2; and then this relates to the power of the word, and the impression made by it upon the heart: q.d. If ye have not only heard of him by the hearing of the ear, but have been effectually taught by the Spirit to know him, and receive his doctrine, Isa_54:13Joh_6:45.
As the truth is in Jesus; as it really is, and hath been taught by Christ himself, both in his doctrine and example, viz. what is the true way of a Christian’s living; as in the following verses: see Joh_17:17Tit_1:1.