
Being married to a builder, I've been exposed to wood glue, pvc glue, laminate flooring glue, tar for shingles, adhesive for Formica, wallpaper glue. Being a mom and occasional crafter, I've bought Elmer's in the gallon size...and used it. I've also used flour and water mixes in a pinch. Burned my fingers with a hot glue gun. Stuck my fingers together with super glue.
Glue sticks things together that would not, without the glue, adhere. Put a piece of paper next to another piece of paper and they just sit there staring at one another. Throw in a few dots of glue, and they are suddenly best friends. Glue changes unlike objects to like ones, or at least into combinations that work. Two dissimilar things become one new thing. It's pretty cool when you think about it.

The "something better" has evolved into complex chemicals that adhere on contact, or need time to cure. Some things need specialty glues. There's a neat website at www. thistothat.com that gives what it calls "glue advice". You choose from what you need to join to something, and what you need to join it to, and the site tells you the best product to use. Cool.
There are drying adhesives, contact adhesives, hot adhesives, pressure sensitive adhesives, reactive adhesives, multi-part and one-part adhesives, natural and synthetic adhesives. They all do basically the same thing: hold things together, and like I earlier, we mostly don't think about them unless they stop working, for one reason or another, or we need them and don't have them.
There is a different kind of glue, too, also easy to take for granted. Have you ever been told that "You are the glue that holds this place together"? We'll call these folks Elmers. Elmers may keep things running smoothly in the office, behind the scenes during a stage production, hold complex family dynamics and relationship in balance. The Not-Elmers involved appreciate the results of the Elmers' work but don't always appreciate the Elmers themselves.
It can be lonely, being the glue. An Elmer sees what others don't, sees the things that need to take place in order to form a cohesive unit out of people who don't always want to be cohesive. Too many folks who just want to do their own things, or who see themselves as so independent that they don't need or want anyone else, and it's difficult drawing everyone together to accomplish a task. And of course, since Elmers are human, their well-intentioned perceptions may not always be accurate.
In the workplace, those who refuse to be glued may get fired. In a family, however, it's not that simple. Sometimes you have to let folks go their own separate ways, obviously, hoping and praying that the adhesive won't dry out completely, that there will be eventual return, reconciliation, restoration. Sometimes. Sometimes not. Meanwhile the Elmer of the family, whoever it is, may feel like he or she failed. "I'm the glue! Why is this happening!"
People depend on Elmers, because they are so capable. So dependable. So efficient at pulling everything and everyone together. People get used to their work, subtly growing lax in their own because subconsciously, they know that the Elmers will take up the slack, fill in the gaps they leave. Elmers can be so good at being the glue that they're actually counterproductive to the long term needs of the unit. In a family, each individual needs to grow, mature, develop--there has to be enough breathing space for that happen, and glue can suffocate. Even when it's doing its job, or the job it thinks it needs to do.
Tricky thing, being the glue. Knowing when to pull back and let things fall apart. Knowing when to fiercely, voraciously slather everything in sight in a last-ditch attempt to stick together. Dealing with the fact that others resent you for the very thing they depend on. Being lonely, wanting someone to draw you in, for a change. When Paul told the Galations "Let us not become weary in doing good, for at the proper time we will reap a harvest if we do not give up" (Galatians 6:9) he was talking to the Elmers.

Mothers are often the glue in families. I prefer to think of us as "hot adhesives."
(c) 2012 Permission to use with acknowledgement of source