On 20 June 1912, he obtained a doctorate from Leuven with a thesis on German stock market regulation: Le régime légal des bourses en Allemagne.

When World War I ignited, Sap fled to Le Havre, where he was the private secretary of Minister Joris Helleputte (agriculture and public works), President of the Boerenbond (Belgian Catholic Farmers Association) from March 1915 until November 1918.

On 5 May 1919, he joined the management of the Catholic Leuvense Volksbank, and on 7 May 1921, he participated in the foundation of the Algemeene Bankvereeniging (ABV) in Antwerp.

As a Council member of the Catholic Boerenbond (E:Belgian Farmers Association) in 1934, he could not avoid the bankruptcy of the Middenkredietkas and the Algemeene Bankvereeniging due to the economic crisis and management issues.

He came into conflict with Paul van Zeeland on economic aspects of the government policy and the National Bank of Belgium (speech of 16 March 1937).