Other comments on this day's readings can be found here.
Reading 1 - 2Samuel 13
David's great sin, although especially forgiven, led to many severe trials during all his remaining years -- trials involving his son Amnon (in the matter of Tamar his sister), his son his son Absalom (guilty of murder and rebellion), Adonijah (the same), and his chief counselor Ahithophel (conspiracy).
It seems quite evident that David, with his many wives and many sons, does not personally teach his children as he should have -- their characters sometimes bearing witness to this shortcoming. See specifically 1Ki 1:6: "His [Adonijah's] father [David, of course] had never interfered with him by asking, 'Why do you behave as you do?' "
Reading 2 - Jeremiah 17:9
"The heart is deceitful above all things and beyond cure. Who can understand it?" (Jer 17:9).
"When we are consciously and deliberately doing God's will, we are happy. When we are not, we are not. In the nature of things it has to be that way. And in the reality of things, it is that way. Analyze it through, and you will find it so. Any other 'pleasure' has to be, and is, self-deception: an ignorant or deliberate self-blinding, a shutting out of reality and consequence, a desperate, warped, juvenile submersion in the present to drown the pain of natural life's meaninglessness and emptiness, to briefly dim the final, inescapable, staring face of eternal death" (GV Growcott).
Reading 3 - Matthew 28:19,20
"Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age" (Mat 28:19,20).
"Unto the End":
"I am with you unto the end": Mat 28:20.
"He loved them unto the end": John 13:1.
"Who shall confirm you unto the end": 1Co 1:8.
"The rejoicing of hope firm unto the end": Heb 3:6.
"Beginning of our confidence steadfast unto the end": Heb 3:14.
"Full assurance of hope unto the end": Heb 6:11.
"Keepeth my works unto the end": Rev 2:26.