Charles H. Spurgeon on Psalms 138:1

With my whole heart. This expression, as in Ps 9:1, points to the surpassing greatness of the benefit received, which filled the whole heart with thankfulness, and did not proceed, as it were, from some particular corner of it. It corresponds also to the greatness of the benefaction, in the expression, before the gods, —demanding of these, whether they would verify their godhead by pointing to any such boon conferred by them on their servants. The benefit which could afford such a demonstration, and give occasion and ground for raillery, must have been a surpassingly great one. —E.W. Hengstenberg.