Consider:
I. What is the strength of a saint. (1) The strength of a saint is the strength of a regenerated man. A regenerated man is not less a man for his regeneration. On the contrary, natural power is brought out in the new birth and sanctified, especially all that is characteristic of human nature. (2) The strength of a man is in his likeness to God, in his being first made and then renewed in the image of God. God in the man is the strength of the man. To obey God and to love both God and His creatures this is the putting forth of the highest strength of man and the highest creative power.
II. The fact that the strength of a saint God has commanded. "Commanded" by what? (1) By what God is and by what He reveals Himself to be. (2) By the relation which God has established between every man and Himself. (3) By a law of loyalty which He has written in the heart. (4) By external verbal law. (5) By the claims of the new kingdom of His grace.
III. Give God your strength. (1) It is treason to withhold it. (2) A full blessing will attend the consecration. (3) In the neglect of this duty there is no valid excuse. The progression of the individual man, like the progression of the race and of the Church, is by antagonism. And this involves incessant spiritual hardship. But in the midst of our conflicts the Almighty God addresses us, saying, "My grace is sufficient for thee, for My strength is made perfect in weakness."
S. Martin, Rain upon the Mown Grass,p. 247.
References: Psalms 68:28. Spurgeon, Evening by Evening,p. 322; A. Watson, Sermons for Sundays, Festivals, and Fasts,3rd series, p. 263.Psalms 68:28; Psalms 68:29. J. M. Neale, Sermons on Passages of the Psalms,p. 190.