Some sensitive Christians feel condemned almost all the time because they are painfully aware of their imperfections. Many, if not most, are upset when they have to deal with imperfection in others! But God, who is entirely perfect in every way without any flaw or blemish in Him, does not get worked up about the imperfections He notices in all of us. That is because He is very realistic and is fully aware that we were born in sin (Ps.51:5) and that we can't help being imperfect in whatever we do. He says that He knows 'our frame' and that we are made of dust. He has compassion on us when we fear and tremble before Him (Ps.103:13,14).
In a sense, we should be very much concerned about our own imperfections, because only then we will seek to press on to perfection (He.6:1). The problem with many Christians these days is that they tell themselves they are 'perfect in Christ' and refuse to be 'negative' by looking at their actual failures and lacks. But when we behold the glory of the Lord (2Co.3:18), if we don't at the same time see our own filthiness in comparison (Is.6:1,5), our transformation into His glory will remain merely imaginary!
At the same time, we must remember that it is not because of our being good enough that God has accepted us as His children, but because He is gracious (Ep.2:8,9). Then we will have a balanced picture where we humbly seek His grace for forgiveness and for transformation into His likeness (He.4:16), without getting into condemnation at the same time.
We also learn to bear with the imperfections in others (Co.3:13), the more we realise how we ourselves are only vessels of His mercy (Ro.9:23). Then we realise that we lost any right we might have had to judge or look down on others when we became recipients of unmerited favour from God (Mt.18:32,33).
While rejoicing in God's grace towards us, what we must also remember is that God will be very much upset with us if we are not pressing on to perfection from our state of imperfection after we have received His grace. That is what He means by saying that if we were lukewarm He would even 'spit us out of His mouth' (Re.3:15,16). Imagine God went to the extent of sacrificing His only Son in order to become able to show us grace, and when we receive grace we just laze around, taking things for granted instead of showing our gratitude towards Him (2Co.5:15)!
On a practical note, even if there may be short ups and downs in our spiritual growth, we need to make sure that the overall trend in our life is upwards. There is forgiveness if we have fallen down and even lost time. But God takes it very seriously if we are not serious about our life with Him, seeking after more of Him, repenting in humility if we grieve Him, learning from our mistakes to do better afterwards, and increasing in our eagerness to fulfil His plans for our lives and to bring honour to His name. He hates it if we become lukewarm and take Him for granted.