SWEW stands for Stichting Waarborgfonds Eigen Woningen and provides the NHG (Nationale Hypotheek Garantie). If you buy a house and close a mortgage, The SWEW offers in this way the warranty to the bank that the loan will be completely repaid. Therefore, the bank gives you a discount on the interest because they have the warranty that they will get the lended money back, even when you are not able to do it, for example with a distressed sale of the house or financial problems. A possible remaining debt will be waived for you. But beware; this is only the case when you satisfy all the conditions.
The conditions are as following:
Don't keep any important secrets when you sign the sales agreement;
Limit the damage for SWEW/NHG: care for a yield as high as possibly;
Co-operate as good as possible when you can no longer afford the mortgage interest.
If your house is in a bad state or when you don't take action (for example, by turning to an estate agent or bank) when you can no longer afford the mortgage, it can be possible that the remaining debt will not be waived. So, always pay attention when it comes to this!