Jamieson, Fausset and Brown on Colossians 4:6

6. with grace--Greek, "IN grace" as its element (Col 3:16; Ep 4:29). Contrast the case of those "of the world" who "therefore speak of the world" (1Jo 4:5). Even the smallest leaf of the believer should be full of the sap of the Holy Spirit (Jr 17:7, 8). His conversation should be cheerful without levity, serious without gloom. Compare Lu 4:22; Joh 7:46, as to Jesus' speech.

seasoned with salt--that is, the savor of fresh and lively spiritual wisdom and earnestness, excluding all "corrupt communication," and also tasteless insipidity (Mt 5:13; Mr 9:50; Ep 4:29). Compare all the sacrifices seasoned with salt (Le 2:13). Not far from Colosse, in Phrygia, there was a salt lake, which gives to the image here the more appropriateness.

how ye ought to answer every man--(1Pe 3:15).