Psalms 38:16

For I said, [hear me]
This he had expressed in prayer to God; he had committed his cause to him, and entreated him that he would hear and answer him; giving this as a reason,

lest [otherwise] they should rejoice over me;
at his misfortunes and calamities, at the continuance of his trouble and distress, both of body and mind;

when my foot slippeth;
as it sometimes did through the corruptions of nature, the temptations of Satan, and the snares of the world; which is more or less the case of all the people of God, who are all subject to slips and falls, though they shall not finally and totally fall away;

they magnify [themselves] against me;
that is, his enemies exulted and triumphed over him: this was what he found by experience; and therefore makes use of it as an argument with God, that he would hear and answer and deliver him out of his trouble, and preserve him from falling.