The "foundation-plan" typically relates to Christ's incarnation, i.e. coming to earth in the flesh to be our Redeemer. This divine plan was set and sealed (guaranteed) before creation.
Foundation: καταβολῆς – katabolé
To sink, sank: יִמַּ֣ךְ – makak
One Hebrew gravity concept occurs in the context of a house so neglected that the roof falls in. The root that the word foundation is derived from is makon: the establishment of a foundation and sinking down.
An Anchor of the Soul
Danby House That by two immutable things, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us: Which hope we have as an anchor of the soul, both sure and stedfast, and which entereth into that …