Temporary faith is an assent to the doctrines of the church, accompanied with profession and joy, but not with a true and abiding joy, such as arises from a consciousness that we are the objects of the divine favor, but from some other cause, whatever it may be, so that it endures only for a time, and in seasons of affliction dies away. Or, it is to assent to the doctrine delivered by the prophets and apostles, to profess it, to glory in it, and to rejoice for a time in the knowledge of it; but not on account of an application of the promise to itself, or on account of a sense of the grace of God in the heart, but for other causes. This definition is drawn from what Christ says in the explanation of the parable of the sower; "He that received the seed into the stony places, the same is he that heareth the word, and anon with joy receiveth it; yet hath he not root in himself, but endureth for a while, for when tribulation or persecution ariseth because of the word, by and by he is offended." (Matt. 13: 20, 21.) The causes of this joy are in a manner infinite, and different in different individuals; yet they are all temporary, and when they fade, the faith that is built upon them, vanishes away. Hypocrites rejoice in hearing the gospel, either because it is new to them, or because it seems to calm their minds, whilst it delivers them from the burdens which men, by their traditions, have imposed upon them, as does the doctrine of christian liberty, justification, etc.; or, because they seek, under its profession, a cloak for their sins, and hope to reap rewards and advantages, both public and private, such as riches, honors, glory, etc., which shows itself when they are called to bear the cross; for then, because they have no root in themselves, they fall away. But hypocrites do not rejoice as true believers, from a sense of the grace of God, and from an application to themselves of the benefits offered in the divine word, which may be regarded as the cause of true and substantial joy in the faithful — the removal of which single cause is sufficient to make their faith temporary.- Zacharias Ursinus, The commentary of Dr. Zacharias Ursinus on the Heidelberg catechism, p. 109
This temporary faith differs from historical only in the joy which accompanies it. Historical faith includes nothing more than mere knowledge; whilst this has joy connected with this knowledge; for these time-serving men "receive the word with joy." The devils believe, historically, and tremble, but they do not rejoice in the knowledge which they have; but rather wish it were extinguished; yea, they do not even profess themselves to be followers of this doctrine, although they know it to be true; but hate and oppose it most bitterly. In men, however, historical faith is sometimes joined with profession, and sometimes not; for men often, whatever may be the causes, profess that truth and religion which they hate. Many also who know the doctrine to be true, still oppose it. Die wollten daß die Bibel im Rhein schwimme. These sin against the Holy Ghost.
Objection: But the devil has often professed Christ. Therefore he cannot be said to hate this doctrine.
Answer: He did not, however, profess Christ from any desire of advancing and promoting his doctrine, but that he might mingle with it his own falsehoods, and thus cause it to be suspected. It is for this reason that Christ commands him to keep silent, as Paul also does in Acts 16:18.
(UPDATE: I see that another version of Ursinus' commentary is on-line here.)