Christ is building a pure heart and a sincere faith in all believers in relation to their keeping all of His commandments. You must take heed, and watch and pray that these good things of righteousness, holiness, and truth are protected and kept. Guard your heart, protect your mind, and fortify your spirit. Watch and pray against sin. Sin would break in, but you need not let him when you have the power of Christ with you, in your heart, to help you stand your guard-duty. This is where I believe many Christians are not watching rightly. It is not just that we need to watch against the thief's intrusion into our hearts, but it is that we will watch against him successfully when we deliberately cultivate fellowship with Christ in our hearts. Yes, it is true that our Lord does appear to "leave us to ourselves", leave us in order to test us to see what is in our hearts, but He never actually leaves us, nor will He ever forsake us in the day of evil, or in the day of trial and testing. But the interesting thing about verse 43 in Matthew 24 is that Christ Himself is the thief in that parable, and you are the master of the house. "Watch therefore, for you do not know what hour your Lord is coming." The Coming of the Lord is said to be like a thief in the night because of the suddenness of it.