Hebrews 4:11

Let us labour therefore to enter into that rest
Not eternal rest; this is not to be entered into now; nor is an entrance into it to be obtained by labour; salvation is not by works; eternal life is a free gift; good works do not go before to prepare heaven for the saints, but follow after: nor is the saints' entrance into it a precarious thing; God has promised it, and provided it for his people; Christ is in the possession of it, and is preparing it for them; and the Spirit of God is working them up for the self same thing, and Christ will give them an abundant entrance into it: but the Gospel rest is here meant, that rest which believers now enter into, and is at this present time for them, ( Hebrews 4:3 Hebrews 4:10 ) and though true believers are entered into it, yet their rest, peace, and joy in Christ, is not full; they enter by degrees into it, and by believing enjoy more of it: and this is to be laboured for by prayer, hearing the word, and attendance on ordinances; and this requires strength, diligence, and industry; and supposes difficulties and discouragements, through the corruptions of the heart, and the temptations of Satan; and this is designed to quicken and awaken a godly jealousy in God's people, over themselves:

lest any man fall after the same example of unbelief;
into the sin of unbelief, and into punishment through it, as the Israelites did; who sinning, their carcasses fell in the wilderness, and they entered not into God's rest, as he swore they should not: true believers may fall into sin, and from a degree of the exercise of grace, and of the steadfastness of the Gospel; but they cannot finally and totally fall away, because they are kept by the power of God; yet they may so fall, as to come short, or at least seem to come short of enjoying the rest and peace of the Gospel state: external professors may fall from the Gospel, and the religion they have professed, and come short of the glory they expected; and fall into just and deserved punishment, in like manner as the unbelieving Israelites did.