Regardless the magnitude of sin-ranging from the tiny white lie to murder-there is a moment when sin is conceived. That sin is always conceived in the mind of the one sinning. James writes, "But each one is tempted when he is drawn away by his own desires and enticed. Then, when desire has conceived, it gives birth to sin; and sin, when it is full-grown, brings forth death" (James 1:14-15). Self-interest and pride is at the root of all sin. It is why while the mantra, "What would Jesus do" is a nice sentiment; it is impossible for humans to accomplish. Jesus was devoid of self-interest or pride (we tend to stockpile it). His sole purpose was to bring honor to His Father. Philippians 2 suggests that Jesus submitted Himself to that mission to the point of death on a cross.
When we begin to "reason in our hearts" like the scribes and Pharisees, we go down the same road as Adam and Eve. When Eve was deceived by Satan, it was because he was able convince her to start "reasoning in her heart" that there was something better for her than God. Our selfish desires, interests, and pride are nothing more than Satan having his way with our minds, just as he did with Eve. We look back over the millennia through our own sin-filled hearts and cast judgment on Eve: "There was only one thing God asked of her!" The truth is, there is only one thing He asks of us but we fail at it every day.
Throughout Mark, chapter 2 the religious leaders "reason in their hearts," they voice their distaste at who Jesus eats with, how He eats, and when He eats! Their self-importance is such a burden to them, they cannot see the One for whom they have waited for hundreds of years is standing in front of them!
We scoff at them. How can they be so blind? Yet our own self-importance finds us at odds with other churches, other believers, different styles of worship, immersed in denominationalism. Adam and Eve and those religious leaders are no more than a reflection of our own prideful behavior when we start to "reason in our hearts." The critical heart is keenly aware of the sin in others because of the kinship they share.