Philippians 4:13

I can do all things
Which must not be understood in the greatest latitude, and without any limitation; for the apostle was not omnipotent, either in himself, or by the power of Christ; nor could he do all things that Christ could do; but it must be restrained to the subject matter treated of: the sense is, that he could be content in every state, and could know how to behave himself in adversity and prosperity, amidst both poverty and plenty; yea, it may be extended to all the duties incumbent on him both as a Christian and as an apostle, as to exercise a conscience void of offence towards God and men; to take the care of all the churches; to labour more abundantly than others in preaching the Gospel; and to bear all afflictions, reproaches, and persecutions for the sake of it; yea, he could willingly and cheerfully endure the most cruel and torturing death for the sake of Christ: all these things he could do, not in his own strength, for no man was more conscious of his own weakness than he was, or knew more of the impotency of human nature; and therefore always directed others to be strong in the Lord, and in, the power of his might, and in the grace that is in Christ, on which he himself always depended, and by which he did what he did; as he adds here, through Christ which strengtheneth me.
The Vulgate Latin and Ethiopic versions leave out the word "Christ", and only read "him"; and so the Alexandrian copy and others; but intend Christ as those that express it: strength to perform duty and to bear sufferings is in Christ, and which he communicates to his people; he strengthens them with strength in their souls, internally, as the word here used signifies; by virtue of which they can do whatever he enjoins them or calls them to, though without him they can do nothing.