Give an easy to follow explanation to these two articles.

ART. 1421. The defense of illegality of contracts is not available to third persons whose interests are not directly affected. Persons entitled to raise defense of illegality or nullity. In voidable (Art. 1397.) and unenforceable contracts (Art. 1408.), third persons are not allowed to bring an action to annul or to assail, as the case may be, said contracts. If the contract isillegal or void, however, even a third person may avail of the defense of illegality or set up its nullity as long as his interest is directly affected by the contract. (see Estanislao vs. GSIS, 60 SCRA 33; see Art. 1177.) EXAMPLE: H, husband, sold his parcel of land to W, his wife. Under the law, husband and wife cannot sell property to each other (Art. 1490.) and such sale is, therefore, illegal and void. (Art. 1409[7].) II. The purpose of the prohibition is to protect third persons who, relying upon supposed property of either spouse, enter into a contract with either of them only to find out that the property relied upon was transferred to the other spouse. Under Article 1421, if T, a third person, became a creditor of H before the transaction, he can question the sale for the reason that his right or interest is directly affected. However, if he became a creditor after the transfer, the defense of illegality is not available to him. (see Cook vs. McMicking, 27 Phil. 10.) ART. 1422. A contract which is the direct result III. of a previous illegal contract, is also void and inexistent. Void contract cannot be novated. This provision is based on the requisites of a valid novation. (see comments and examples under Art. 1298.) An illegal contract is void and inexistent and cannot, therefore, give rise to a valid contract. For example, a contract of repurchase is dependent on the validity of the contract of sale. If the latter is itself void because the seller is not the owner, the former is also void because it presupposes a valid contract of sale between the same parties