1. Consider the Lord (Hebrews 3:1-6)
2. Consider His Word (3:7-11)
3. Consider your heart (3:12-19).
The writer of Hebrews is warning his readers of a powerful virus that is already in the heart of unbelievers and threatens the spiritual lives of God's saints: namely the disease of unbelief. In citing a historical example from the days of the first generation of Israelites coming out of Egypt under Moses, the writer of Hebrews demonstrates the results of not taking the prescription for strong faith.
The first stage of the disease of unbelief begins to set in: hardness of heart (Hebrews 3:12-15). The second stage following hardness of heart is spiritual blindness (3:16-17) with the final stage that demonstrates the lack of true saving faith, namely inability to enter into God's rest of salvation (3:18-19). The frightening reality of these warnings about unbelief is that true believers can experience for seasons at a time the first two stages of hardness of heart and spiritual blindness. Only the grace of God in God's Fatherly discipline can prevent them from falling away from salvation. (compare Hebrews 12:5-8)
To illustrate this from the Old Testament, whenever you read Jeremiah 43-44 you see God the Father attempting yet again to convince the left over people of Judah to repent and turn to Him. However the people refuse and in perhaps one of the most blatant acts of rebellion recorded in God's Word, actually tell Jeremiah that they will not listen to God. They refuse Jeremiah's God-given prescription for strong faith. The result? God does to them as described in Romans 1 - He hands them over to the depravity of their desires and mindset.
The worse form of judgment is whenever God gives us what we want. The people's refusal to receive the remedy demonstrated their lost condition. Because of their refusal, God passed over them in judgment, even though He desired to show mercy. Jeremiah 45 is another prophecy written prior to the events of Jeremiah 43-44 that demonstrates how much God has issued repeated warnings and given space for repentance. May you and I receive God's prescription for strong faith: consider the Lord, His word and your heart.