Foolish talking and jesting are not the ways in which Christian cheerfulness should express itself, but rather "giving of thanks" (Eph. 5:4). Religion is the source of joy and gladness, but its joy is expressed in a religious way, in thanksgiving and praise.
Charles HodgeHe [man] knows that when he is not what he ought to be; when he does what he ought not to do; or omits what he ought to do, he is chargeable with sin
Charles Hodge