Yes, sanctification begins at redemption, but salvation is not a "process for us to maintain". The problem with that idea is the New Testament. Scripture is very clear that salvation is a free gift...that is has nothing to do with us at all...it is won and given to us by Christ, a process won in an instant in time (the cross) and received in another instant in time (regeneration). The proof of that regeneration is the process that follows...sanctification. Some people put up their hands and say they're Christians, but they don't grow, don't even try, and use their 'freedom' as license to sin. They have not been truly born again.
Sanctification is man working in cooperation with God as he puts sin to death every day and walks closer to God. Salvation is God acting alone save us. biggandyys illustration is correct. The thing with salvation/sanctification is that if salvation relied on our walk, we would fail. Salvation comes only from perfection...which we have in Christ. So it is just as well that redemption comes to us in the form of a free gift already won! Sanctification, because it is a lifelong process in which God helps us get up again and again and again and walk forwards after every stumble...it is not only something we can do, but are required to do.
The Israelites were saved out of Egypt. But how many pleased God afterwards? So God reserves the right to judge His own people. We must continue to lead a pleasing life to the Lord otherwise we will be cut off...just as they were. This truth maintains the proper fear to remain in obedience even when we reach a dead end...or what seems to be a dead end! ;)
But how many will have the proper fear rather than take God's salvation for a "fait-accompli" (done deal) just as the Israelites did who died in the wilderness. Have we not learned anything from them? There are too numerous instances where this is shown in the New Testament as well. God is always faithful..His people are not. We must be found to be faithful to enter into the promises of God. The "wild card" so to speak, is us! That is why we exhort each other daily to not fall short of His grace nor frustrate the grace that we have begun the race with. We are to run so as to win...always fearing the Lord...and never putting any confidence in the flesh. We cannot sit on our laurels for a past repentance and acceptance. We must continue to seek and abide in Christ if we are to pass through the trials in a satisfactory fashion. If God did not spare the natural branches neither will He spare the late comers...sobering thoughts indeed!
Here's a couple of scriptures to consider.
And I am certain that God, who began the good work within you, will continue his work until it is finally finished on the day when Christ Jesus returns.
Phil 1:6 (NLT)
We do this by keeping our eyes on Jesus, the champion who initiates and perfects our faith. Because of the joy awaiting him, he endured the cross, disregarding its shame. Now he is seated in the place of honor beside God’s throne.
Heb 12:2 (NLT)
God is certainly faithful!!! And He will judge us faithfully and truthfully. All men will reap what they have sown.