This devotional could be confusing if not read and applied properly with the truth that Jesus has already overcome. I have many devotionals like this and get the same sort of message that leaves out the "how too". "My Utmost For His Highest" is a lot like this one as well. Also others I've used over the years.
For instance in reference to certain strong holds of sin the writer is correct in saying some sins can be like (I say - feel like) chariots of iron in our constitution. He then says "we must overcome them they are very strong we are very weak; yet in the name of God we must master them and we will." I see the need to reference it is in the name of Jesus who has already overcome sin., that we submit to that truth BY FAITH and THEN we will see the victory over them come to fruition in our lives.
Spurgeon goes on to say; if one sin has dominion of us we are not the Lord's free men.,a man who is held by only one chain is still captive. There is no going to heaven with one sin ruling within us, for of the saints it is said, sin shall not have dominion over you.
But I see from Scripture that we ARE already have been made the Lord's free men because of Jesus., and the work we must do is by faith believing., it is then the truth will come to fruition in our lives. We NEED the rest of the verse about sin not having dominion in our lives..(because) you are not under law but under grace. Grace (unmerited love and favor) gives the truth and freedom to walk out what Christ has already done in our lives.
It is not our strength and will power that will win over the power of sin., but it is by faith in the Son of God who loves us and gave Himself for us that gives us the power over sin in our lives.
Now Spurgeon might be saying this but it's hidden to me by what was not said. That faith in the finished work of Jesus is what gives the victory., not my power of will to do it but by faith in Him and what He has already done. This makes all the difference. Only then it is possible to say; UP, then and slay every Canaanite, and break to shivers every chariot of iron because the LORD of Hosts is with us and nothing can resist His sin-destroying power!