Many people in Jesus' day followed Him because they were enamored with the signs...they were given food to eat, they saw others whose sight was restored or the lame who could walk again. What might they hope to glean by following Him? I'm not saying all the people felt this way. There were always some who recognized more than the physical and truly came to Him with all their heart with a desire to follow Him.
On one hand His gift to us is free. On the other we must act on it. This is where He knows the intents of man.
We can say we believe in Christ and go to church and say the right words, but God knows our intent. It's why, I'm convinced, there will be a small number of people who really enter into the kingdom. Even I have to wonder at times about my intent...
God has known the intents of man for a very long time:
Genesis 6:5 - Then the Lord saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually.