When you see a command in the New Testament; it is not there for you to fulfill in order to be righteous. (Matt. 5:17; Romans 10:4) Your Father has put these things there to protect you from the negative consequences of wrong actions.
For example: when He instructs you on where to put your thoughts, it is not for the purpose of controlling your mind. He knows that where the mind goes; the man or woman follows. (Isaiah 26:3; Phil. 4:8) Therefore, He advises you because He desires you to experience all of His blessings.
While it is true that He will never leave you; your husband or wife may. Get the point? I encourage you to view the instructions of the New Covenant as advice from a loving Father who desires nothing but the best for His children. You are so loved.