What I am taking up now are these words from Paul to Timothy:

Take pains with these things; be absorbed in them, so that your progress will be evident to all. Pay close attention to yourself and to your teaching; persevere in these things, for as you do this you will ensure salvation both for yourself and for those who hear you. (1 Timothy 4:16)

I cannot help but contrast "you will ensure your salvation," which seemingly implies that salvation is difficult to obtain, with these earlier words from the same letter, "... the living God, who is the Savior of all men, especially of believers." (1 Timothy 4:10) The former words of Paul seemingly suggested universalism, while these suggest salvation by works. Neither conclusion was intended by Paul.

While some, at this point, might make appeals to Calvin or Arminius, my plan is to go to some related Scriptures and see what practical points Paul is making. I begin with Hebrews 10:

Therefore, do not throw away your confidence, which has a great reward. For you have need of endurance, so that when you have done the will of God, you may receive what was promised. 

For yet in a very little while, He who is coming will come, and will not delay. But My righteous one shall live by faith; And if he shrinks back, My soul has no pleasure in him. 

But we are not of those who shrink back to destruction, but of those who have faith to the preserving of the soul. (Hebrews 10:35-39)

I see a parallel teaching in Paul's words to Timothy and these words from the author of Hebrews. I want you to note the last line here, "We are not of those who shrink back, but of those who have faith to the preserving of the soul." The author to the first century Messianic Jews and his readers knew that they were saved. But notice that their salvation implied a steadfastness in the face of trials. They had "faith to the preserving of the soul" and were, therefore, "not of those who shrink back."

Here is what Paul wrote to the Colossians:

And although you were formerly alienated and hostile in mind, engaged in evil deeds, yet He has now reconciled you in His fleshly body through death, in order to present you before Him holy and blameless and beyond reproach— if indeed you continue in the faith firmly established and steadfast, and not moved away from the hope of the gospel that you have heard, which was proclaimed in all creation under heaven, and of which I, Paul, was made a minister. (Colossians 1:21-23)

Paul here states with confidence that his readers "were formally alienate and hostile" and that Jesus "has now reconciled you." Paul here and elsewhere also makes clear that it is Jesus and his life, death, and resurrection that have provided salvation for us. So why does Paul tack on "if you continue in the faith?"

The first fact to lay down from the evidence is that it is possible to know that we are saved. The author of Hebrews makes this clear. As does Paul in Romans:

The Spirit Himself testifies with our spirit that we are children of God, (Romans 8:16)

It is this "assurance of salvation" that Paul has advised Timothy to obtain for himself and others when he writes, "you will ensure salvation."

The second fact to lay down from the evidence is that we need to emphasize the effect of faith in the life of the believer. A person is a Christian by faith:

Now faith is the assurance of things hoped for, the conviction of things not seen. For by it the men of old gained approval. (Hebrews 11:1-2)

For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast. For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them. (Ephesians 2:8-10)

Faith is not merely belief or intellectual assent to understood truth. It is also a force for change in the life of the saint. It is the connection with God and His Holy Spirit that is expected to yield fruit. 

The third fact to lay down is that there will be those who have good starts and bad finishes. Paul wrote of Hymanaeus and Alexander as examples. The achieving of faith is both a work of God and a process. Modern Christianity likes to be either/or about this:

Would you like to go to heaven?

Sure!

Say this prayer asking Jesus into your heart and you will get to go to heaven.

OK! I'm now heaven bound.

But is he heaven bound? Besides appealing to self-interest, the above illustration sees salvation as either there are not there. The New Testament is more transitional:

And He said to them, “Do you not understand this parable? How will you understand all the parables? 

“The sower sows the word. 

“These are the ones who are beside the road where the word is sown; and when they hear, immediately Satan comes and takes away the word which has been sown in them. 

“In a similar way these are the ones on whom seed was sown on the rocky places, who, when they hear the word, immediately receive it with joy; and they have no firm root in themselves, but are only temporary; then, when affliction or persecution arises because of the word, immediately they fall away. 

“And others are the ones on whom seed was sown among the thorns; these are the ones who have heard the word, but the worries of the world, and the deceitfulness of riches, and the desires for other things enter in and choke the word, and it becomes unfruitful. 

“And those are the ones on whom seed was sown on the good soil; and they hear the word and accept it and bear fruit, thirty, sixty, and a hundredfold.” (Mark 4:13-20)

Some teachers try to assure people of their salvation by giving them a "prayer reference" as a point in time when they trusted the Messiah. The New Testament, however, asks the individual to look for assurance in the heart and by fruit in the life. There are times when a person only needs to pray and make a final commitment. There are other times when more seed needs to be sown, or hard ground broken up, or rocks removed, or weeds pulled. As tests of faith come and go, your assurance will grow. As your heart loses its hardness and love for God and desire for His Kingdom emerges, you assurance will grow. Ask, seek, and knock, and such will come to you.

In light of this, can a man or woman of faith have periods of grievous sin? Yes, they can! Faith does not bring perfection and seeds sown prior to our being saved often grow their own grievous fruit. I know many who have walked through such periods and have emerged stronger than before. During their time of sin, they grieved over their lack of power and, in a curious way, placed their hope in Jesus to deliver them from the power currently entrapping them. Sin was there, but so was faith. Eventually faith won and deliverance from the sin achieved.

<>< Test everything. Cling to what is good. ><>