When the jailor said, "Sirs, What must I do to be saved?" Paul did not so much as once ask him, What is your motive in this question? Do you design the glory of God, in the salvation of your soul? He had more sense; he knew that such questions as these would have been but foolish talk about, instead of a sufficient relief to so weighty a question as this. Wherefore, since this poor wretch lacked salvation by Jesus Christ, the salvation from hell and death, which he knew, now, was due to him for the sins that he had committed, Paul tells him, as the poor condemned sinner that he was, to proceed still in this his way of self-seeking, saying, "Believe on the Lord Jesus Christ, and thou shalt be saved" (Acts 16:30-32). (pg. 37)
Please note that even though the deliverance of our souls from damnation may be our motive to turn to Christ, we soon learn in his school the purpose of our salvation:
I know that afterwards you will desire to glorify Christ by walking in the way of his precepts; but at present you want life; the avenger of blood is behind you, and the devil like a roaring lion is behind you; well, come now, and obtain life from these; and when you have obtained some comfortable persuasion that you are made partaker of life by Christ, then, and not till then, you will say, "Bless the Lord, O my soul, and all that is within me bless his holy name. Bless the Lord, O my soul, and forget not all his benefits: who forgiveth all thine iniquities, who healeth all thy diseases; who redeemeth thy life from destruction; who crowneth thee with lovingkindness and tender mercies" (Psa 103:1-4). (ibid)
In other words, don't let the thought that you might have "impure motives" keep you from embracing the salvation that is found in Christ Jesus.