Saints, I want to exhort you to, ALL DAY, EVERY DAY, be trusting and relying on what Jesus did for you at the cross!!
Hebrews 3:13 says - "but exhort ye one another every day, while the To-day is called, that none of you may be hardened by the deceitfulness of the sin," (Young's Literal Translation).
This is powerful brothers and sisters! This verse is saying that we ought to exhort (admonish, exhort, console, and encourage) one another daily, but with the idea of a particular admonishment, or exhortation; not just, try cheering one another up with kind and motivational words...
Because the apostle Paul sometimes uses a negative argument to bring about a positive result, the verse ends with "that none of you be hardened by the deceitfulness of (the) sin", with the definite article before the word "sin" (which is why I'm showing the YLT rendering of the verse).
The word "sin" here is NOT talking about our actions! Although our actions can definitely harden our heart, that's not in context what's being said. Paul is referring to the "sin" of unbelief (not trusting in the Gospel), as the "sin" that will harden our heart.
The definite article (the word "the") before the word "sin" is introducing a noun or noun phrase (not verb) and is implying that the THING (not action) mentioned has already been mentioned, is common knowledge, or is ABOUT TO BE DEFINED... If we keep reading through Hebrews 3, we'll see that the Jews could not enter into God's rest because of unbelief, even though they were the children of God!!! So again, the "sin" being DEFINED here is the "sin" of unbelief. Not our actions, but rather our inaction or passiveness to rely on the cross.
Verses 3:17-18 clearly DEFINE this by saying; 3:17 - "But with whom was he grieved forty years? was it not with them that had SINNED, whose carcases fell in the wilderness? 3:18 And to whom sware he that they should not enter into his rest, but to them that BELIEVED NOT?...
What's more (without separating chapter and verse), chapter 4:1-2 go on to define the specific "believing not" as "not mixing faith with the Gospel".
Paul's heed, or warning in 4:1-2 - "Let us therefore fear" is implying that if the Jews, as children of God, could not enter into a promise of God because of "not mixing faith with the Gospel", then we as well can fall short of the promises of God, even as believers...
On the contrary, Hebrews 3:14 states: "For we are made PARTAKERS of Christ (partakers of His resurrection, victorious life), IF we hold the beginning of our confidence stedfast unto the end;" meaning if we keep our faith and hope in what Jesus did.
So the specific exhortation we should exhort one another with is: have your faith (trust, reliance, and dependency) in what Jesus did for you at the cross for your everyday victory!!! Experience God by faith in the finished work of Jesus!!!
After all, John 5:4 says: "this is the victory that is overcoming the world, your "faith". (Referring to WHAT you believe; which is, the sacrifice and resurrection of Jesus... Hallelujah!!!)