Perhaps it's human nature to boast. Even the most humble among us want to be appreciated and valued for our contribution. We want others to notice what we bring to the group and affirm our unique skills and talents. Sometimes we might help others notice our efforts, either through direct bragging or the way many people disguise it as false modesty.
In either case, we're wanting to take credit for something that we've created, built, selected, achieved, accomplished, or won. With our salvation, there's no way we can take any credit whatsoever. All of us have sinned and fallen short of the glory of God. We can't earn his favour or save ourselves.
Jesus came to do what we could not. Through his sacrifice, we have eternal life simply by accepting his free gift. There's nothing we can do to buy it, or earn it. We are all equal recipients of God's love and grace.