In the smallest and most general of nutshells, the Church teaches that Holy Orders configures a man in a special way to Christ for the purpose of representing God before the faithful – by preaching the faith, administering the sacraments, and governing the Church – and of representing the faithful before God by offering the Eucharistic sacrifice (or, in the case of deacons, assisting at the sacrifice in a distinctive way).
The traditional theological expression is that the sacrament of Orders imparts a “character” on a man that can never be removed, in this life or the next. In other words, once a deacon, priest, or bishop – always a deacon, priest, or bishop.
Even a cleric who is formally laicized retains the character of the sacrament – he’s simply not allowed to exercise the ministry.
Only men (as in males) can be ordained and there are other less-integral requirements as well – e.g., only unmarried men are ordained bishops, and in the West this is normally also the case with priests, with some relatively rare exceptions.
With that said, I don’t think it would even be quite right to say that any unmarried adult Catholic man can be ordained. This distinguishes Holy Orders from other sacraments – for example, I’m fairly certain that any properly-disposed Catholic has a canonical right to receive Communion, or to have his confession heard.
But no one has a right to Holy Orders. The Church (and ultimately God) calls particular men to the hierarchy, and the reason why some are called and others are not is to some extent a mystery.
As far as the emotional significance of the sacrament goes, I really couldn’t say since I’m not ordained. In general though I’d guess that the subjective effect of any sacrament is likely to depend on a number of factors, from things as simple as how well you’ve been sleeping lately on the one hand, to the quality and quantity of your preparation for the sacrament on the other hand – not to mention the extent to which you mature in the mission of the sacrament by remaining faithful to it over time.
